internals: update MSRV to 1.74

diff --git a/internals/Cargo.toml b/internals/Cargo.toml
index 68e8f012..633acf4f 100644
--- a/internals/Cargo.toml
+++ b/internals/Cargo.toml
@@ -10,7 +10,7 @@ categories = ["cryptography::cryptocurrencies", "no-std"]
 keywords = ["internal"]
 readme = "README.md"
 edition = "2021"
-rust-version = "1.63.0"
+rust-version = "1.74.0"
 exclude = ["tests", "contrib"]
 
 [features]
diff --git a/internals/build.rs b/internals/build.rs
index fff95c4b..a8407015 100644
--- a/internals/build.rs
+++ b/internals/build.rs
@@ -51,10 +51,10 @@ fn write_macro(mut macro_file: impl io::Write, msrv_minor: u64, minor: u64) -> i
     writeln!(macro_file, "/// Example:")?;
     writeln!(macro_file, "/// ```")?;
     writeln!(macro_file, "/// bitcoin_internals::rust_version! {{")?;
-    writeln!(macro_file, "///     if >= 1.70 {{")?;
-    writeln!(macro_file, "///         println!(\"This is Rust 1.70+\");")?;
+    writeln!(macro_file, "///     if >= 1.78 {{")?;
+    writeln!(macro_file, "///         println!(\"This is Rust 1.78+\");")?;
     writeln!(macro_file, "///     }} else {{")?;
-    writeln!(macro_file, "///         println!(\"This is Rust < 1.70\");")?;
+    writeln!(macro_file, "///         println!(\"This is Rust < 1.78\");")?;
     writeln!(macro_file, "///     }}")?;
     writeln!(macro_file, "/// }}")?;
     writeln!(macro_file, "/// ```")?;
diff --git a/internals/src/array_vec.rs b/internals/src/array_vec.rs
index 830ba598..c0a036d8 100644
--- a/internals/src/array_vec.rs
+++ b/internals/src/array_vec.rs
@@ -12,8 +12,6 @@ pub use safety_boundary::ArrayVec;
 mod safety_boundary {
     use core::mem::MaybeUninit;
 
-    use crate::const_tools::cond_const;
-
     /// A growable contiguous collection backed by array.
     #[derive(Copy)]
     pub struct ArrayVec<T: Copy, const CAP: usize> {
@@ -43,14 +41,11 @@ mod safety_boundary {
             Self { len: slice.len(), data }
         }
 
-        // from_raw_parts is const-unstable until 1.64
-        cond_const! {
-            /// Returns a reference to the underlying data.
-            #[allow(clippy::incompatible_msrv)] // Clippy doesn't play nicely with `cond_const!`.
-            pub const(in 1.64) fn as_slice(&self) -> &[T] {
-                let ptr = &self.data as *const _ as *const T;
-                unsafe { core::slice::from_raw_parts(ptr, self.len) }
-            }
+        /// Returns a reference to the underlying data.
+        #[allow(clippy::incompatible_msrv)] // Clippy doesn't play nicely with `cond_const!`.
+        pub const fn as_slice(&self) -> &[T] {
+            let ptr = &self.data as *const _ as *const T;
+            unsafe { core::slice::from_raw_parts(ptr, self.len) }
         }
 
         /// Returns a mutable reference to the underlying data.
diff --git a/io/src/bridge.rs b/io/src/bridge.rs
index f82a8720..52a47694 100644
--- a/io/src/bridge.rs
+++ b/io/src/bridge.rs
@@ -253,40 +253,20 @@ macro_rules! impl_our {
     };
 }
 
-rust_version! {
-    if >= 1.72 {
-        impl_our! {
-            impl<R: std::io::Read> Read for std::io::BufReader<R> where R: ?Sized
-        }
-
-        impl_our! {
-            impl<R: std::io::Read> BufRead for std::io::BufReader<R> where R: ?Sized
-        }
-
-        impl_our! {
-            impl<W: std::io::Write> Write for std::io::BufWriter<W> where W: ?Sized
-        }
-
-        impl_our! {
-            impl<W: std::io::Write> Write for std::io::LineWriter<W> where W: ?Sized
-        }
-    } else {
-        impl_our! {
-            impl<R: std::io::Read> Read for std::io::BufReader<R>
-        }
+impl_our! {
+    impl<R: std::io::Read> Read for std::io::BufReader<R> where R: ?Sized
+}
 
-        impl_our! {
-            impl<R: std::io::Read> BufRead for std::io::BufReader<R>
-        }
+impl_our! {
+    impl<R: std::io::Read> BufRead for std::io::BufReader<R> where R: ?Sized
+}
 
-        impl_our! {
-            impl<W: std::io::Write> Write for std::io::BufWriter<W>
-        }
+impl_our! {
+    impl<W: std::io::Write> Write for std::io::BufWriter<W> where W: ?Sized
+}
 
-        impl_our! {
-            impl<W: std::io::Write> Write for std::io::LineWriter<W>
-        }
-    }
+impl_our! {
+    impl<W: std::io::Write> Write for std::io::LineWriter<W> where W: ?Sized
 }
 
 impl std::io::Write for super::Sink {
@@ -344,25 +324,21 @@ impl_our! {
     impl BufRead for std::io::Empty
 }
 
-rust_version! {
-    if >= 1.73 {
-        impl_our! {
-            impl Write for std::io::Empty
-        }
+impl_our! {
+    impl Write for std::io::Empty
+}
 
-        // No idea why &Empty impls Write but not Read + BufRead
-        impl_our! {
-            impl Write for &'_ std::io::Empty
-        }
+// No idea why &Empty impls Write but not Read + BufRead
+impl_our! {
+    impl Write for &'_ std::io::Empty
+}
 
-        impl_our! {
-            impl Read for std::sync::Arc<std::fs::File>
-        }
+impl_our! {
+    impl Read for std::sync::Arc<std::fs::File>
+}
 
-        impl_our! {
-            impl Write for std::sync::Arc<std::fs::File>
-        }
-    }
+impl_our! {
+    impl Write for std::sync::Arc<std::fs::File>
 }
 
 impl_our! {