Fix all Rust clippy warnings that were causing CI failures when built
with RUSTFLAGS=-Dwarnings. Changes include:
- Replace derivable_impls with derive macros for BlockBody, Network, etc.
- Use div_ceil() instead of manual implementation
- Fix should_implement_trait by renaming from_str to parse
- Add type aliases for type_complexity warnings
- Use or_default(), is_some_and(), is_multiple_of() where appropriate
- Remove needless borrows and redundant closures
- Fix manual_strip with strip_prefix()
- Add allow attributes for intentional patterns (too_many_arguments,
needless_range_loop in cryptographic code, assertions_on_constants)
- Remove unused imports, mut bindings, and dead code in tests
5c643af64c