Resolve -D warnings under Rust 1.95 clippy:
- simd_cdc.rs: use compound assignment in unit test; document and
scope-allow too_many_arguments on the SIMD inner-loop helper
(each parameter is a distinct cursor/limit on the hot path).
- merkle.rs: drop `(usize).max(0)` which is always \u22650.
- benches: factor `fn(usize) -> Vec<u8>` into a `DataGen` type alias
to satisfy clippy::type_complexity.
No behavioral changes; all workspace tests pass.
Omar Sobh
bb44edcf90