rust-bitcoin

Improve codec methods implementation

Use Rust's Option methods and Pattern matching to collapse if_let_else
constructs in the `read_limit` method implementation, this maintains a
clearer and concise usage of the `Option<T>` API.

Leverage `Option<T>::is_some_and` method for the `advance` method impl,
which proceeds to propagate to `Encoder::advance` if the encoder is
`Some(T)` and returns false if the encoder is `None`.

Update API files

Simplify `Decodable` trait

The `Decodable` trait already required that a decoder can be created
without providing any extra arguments and it required that the output of
the decoder is `Self`, implying that no decoder can be reused for
different types.

We observe that simply requiring that `Decoder` impls `Default` is
practically the same thing - requires constructibility without
arguments. By bounding `Decoder` on `Default` in addition to `Decoder`
and providing a default implementation of the method we simplify the
implementations: they now only need to impl `Default` which often can be
derived and specify the associated decoder type.

Remove now-useless overrides of `decoder`

The previous commit added a default impl for the `decoder` method which
renders the existing ones uselsess overrides. This commit simply removes
all of them.

Update API files

p2p: add V1MessageHeader constructor

Adds a constructor to `V1MessageHeader` which also computes the 4 byte
checksum as defined by protocol docs. This constructor is used to
compose a network header that can be transmitted over the network stream.

Any network message (payload) must be directly preceded in the network
stream by a header. In that way, the receiving client knows how many
bytes to read, and what message to interpret.

A working code example might be a Pong response:
```
let message = bitcoin_p2p_messages::message::Pong(nonce);
let msg_header = V1MessageHeader::new(magic, &message, "pong");

// write the header to stream
encoding::encode_to_writer(&msg_header, &stream);

// write message to stream
encoding::encode_to_writer(&message, &stream);
```

Note that Currently, CommandString wraps a Cow<'static, str>, so the
lifetime of `cmd` must match the static lifetime. However, the protocol
documents define this as a 12 byte field, so this can and should be
changed at some point.

The fields defined in `V1MessageHeader` is the first four fields of a
message structure. An example given in the docs of message header is
given as:

```
Message Header:
F9 BE B4 D9 - Main network magic bytes
76 65 72 73 69 6F 6E 00 00 00 00 00 - "version" command
64 00 00 00 - Payload is 100 bytes long
35 8d 49 32 - payload checksum (byte order)
```

bitcoin: cut down on exact_features test matrixes

The Github CI runner is timing out when running all the feature sets
on the older MSRV compiler. The current list of exact_features in the
bitcoin crate was a conserative "include everything" when we switched
over to cargo-rbmt. This cuts it down ~50% and focuses on core
interactions we want to always cover. This puts more responsibilites on
cargo-rbmt's random feature subsets it runs on every commit.

Re-name consensus_encoding main traits

When we did the first implementation of the `consensus_encoding` crate
we used the same names for the public traits as the old encoding code.

In hindsight we should have used the more Rusty terms `Encode` and
`Decode` instead of `Encodable` and `Decodable`.

Bonus points the new names are easier to spell.

Do trivial-ish rename. Leave the `EncodableBytesIter` as is because
the fix to it is non-trivial. Leave the old encoding traits as they
are because they are destined for the grave very soon anyways.

fuzz: Migrate p2p fuzz targets to new encoding

p2p: remove deprecated encoders in V1NetworkMessage constructor

`payload.consensus_encode()` is deprecated. Replace with
newer sans/IO `hashes::encode_to_engine()`.

Also, updated the doc comment now that encode no longer has a panic
path.

Move import

There is an unrelated lint warning, no clue how it started showing up
but its a trivial fix. Move import from one feature gated scope to
another.

Implement Consensus Encoding for V2NetworkMessage

Implement new consensus encoding traits for the V2NetworkMessage
struct, to be sent as a message across the Bitcoin Network P2P.

This is part of the ongoing attempt to drop bitcoin as a dependency
from `bitcoin-p2p-messages` crate.

Constructs the Encoder and Decoder types for the encoding and
deserialization of the V2NetworkMessage, introduces the
`V2NetworkMessageDecoderError` to report errors encountered while
enc/decoding the message.

Co-authored-by: rustaceanrob <rob.netzke@gmail.com>

units: scrub encoder/decoder layout

Improve hex codec test coverage

Update API files

Move transaction encoding tests to primitives/tests/encoding.rs

This change moves transaction consensus encoding and decoding tests,
along with shared helpers and constants, into a dedicated test file.
Removes the FIXME comment that requested this change.

The assert_eq! on the no-witnesses error is replaced with matches!
on the outer error type due to visibility constraints.

Drop use of deprecated methods

In sign-tx-segwit example, the deprecated `public_key` method was
still being used, not reflecting the now recommended `to_public_key`
method.

This patch drops the use of the deprecated method for the now recommended
method by the API.

Remove useless `Option`s in encoders

The `Encoder` contract states that implementors are not obligated to
make the state after `false` was returned defined, however they so far
did so anyway and this was even tested. This was a waste of performance
and complication of the code that would get amplified with multiple such
encoders chained as each would have to track the final state.

This change removes all those `Option`s, associated tests and in
addition replaces `&[]` return with panic in invalid state of a
composite encoder.

Update API files

Update API files

Replace upper-lower serde parsing with from_unprefixed_hex

The U256 deserialize impl manually splits a known-length string into
upper and lower halves. While this functions correctly, it's a
needless reimplementation of the same functionality present in U256's
from_unprefixed_hex function.

Replace the manual split of strings in U256 deserialize with a single
call to from_unprefixed_hex.

Remove visit_bytes from U256 serde

In the U256 serde deserialize impl, a visitor struct is defined inside
of an is_human_readable() condition block. The visit_bytes function in
this block can't be used as the data is human readable and thus only
visit_str is required. As such, it can be removed.

Remove the visit_bytes from the HexVisitor struct in U256 Deserialize.

Update API files

Update API files

units: Add #[inline] attributes to simple functions

Where functions merely delegate to other functions, or only perform
trivial operations, they should be annotated with #[inline] to nudge
the compiler towards improving performance by inlining them.

Add #[inline] to trivial functions in all modules.