Adopt Rust 1.97 integer APIs and Cargo warning policy (#29048)
## Summary
- Use the integer bit APIs stabilized in Rust 1.97 for packed node
indices, token capacity, rule iteration, and type-variable support sets.
- Use Cargo's warning policy in our native and WASM Clippy checks,
keeping warnings fatal without changing compiler flags and invalidating
the build cache. Update the contributing guides to match.
Preserves the Rust 1.97 MSRV. The warning policy change follows
https://github.com/astral-sh/uv/pull/22122.
