Update Rust toolchain to 1.96 and MSRV to 1.94 (#25443)

## Summary

- Update the pinned Rust toolchain from 1.95 to 1.96.
- Raise Ruff's minimum supported Rust version from 1.93 to 1.94,
following the N-2 policy.
- Replace the now-unnecessary `zip_opt` helper with `Option::zip`, as
Rust 1.96's Clippy flags the manual implementation.

## Test plan

`cargo clippy --workspace --all-targets --all-features -- -D warnings`