BitBox02 firmware

This commit is a routine code reorganization: it moves two small helper modules (one for generating random bytes, one for salting/hashing data) from an existing Rust crate into a new shared workspace crate named bitbox-core-utils. The actual logic, algorithms, and behavior are copied unchanged; only the file paths and import names are updated. There is no indication this fixes or introduces a security vulnerability.

This commit simply moves a test-only fake random number generator from one internal Rust module to another. The code is identical and is only used in automated tests running on a developer's computer, not in the real BitBox02 hardware wallet firmware. There is no security issue.

This commit changes how the BitBox02 hardware wallet generates random numbers used to create secret keys and encrypt stored data. Previously, the firmware used a single 32-byte random value from the microcontroller. After this change, it mixes three sources: the microcontroller's random generator, the secure chip's random generator, and a fixed 32-byte 'factory randomness' value stored in a special flash memory location. The commit also adds a factory script to write that fixed value into devices during production. The change is a defensive hardening measure, not a fix for an active bug, but it introduces a new dependency: if the factory randomness is not actually random or is reused across devices, it could weaken security instead of strengthening it.

This commit fixes a Rust build configuration issue so that the project's automated tests can run on a normal computer. It moves a required feature flag for the 'hex_lit' library from individual sub-crates to the shared workspace configuration. There is no indication this is a security fix or that it changes any runtime behavior on the actual BitBox02 device.

This commit changes how the BitBox02 hardware wallet warns users about very large Ethereum transaction data and typed messages. Previously, large transaction data was shown only as a byte count with the message 'too large to display.' Now the device shows a preview of the actual hex data (up to the screen limit, with a '...' truncation indicator) and adds a warning screen saying the value is too large to display in full. The change also reuses the same truncation logic already used for EIP-712 typed messages, so both flows behave consistently. The commit does not fix a vulnerability, but it improves the user's ability to inspect what they are signing.

This commit is a code-quality refactor for unit tests only. It introduces a small Rust helper macro called async_test::test that lets developers write async test functions directly, instead of manually wrapping async code in a block_on() call. The change touches many test files but does not alter any production firmware behavior, user-facing functionality, or security logic.