Update Rust toolchain and dependencies

[alshdavid]

Summary

No code changes were required. Only transitive dependency updates in Cargo.lock.

Toolchain

• rust-toolchain: Already at 1.99.0 (latest stable) — no change needed
• rust-version (MSRV): Not explicitly set in Cargo.toml
• CI workflows: Use rustup install stable which resolves to 1.99.0 — no change needed

Dependencies

No direct dependencies needed updating (all up to date per cargo outdated).

Transitive dependency updates (Cargo.lock only)

Crate	Old	New
pest	2.9.2	2.9.3
pest_derive	2.9.2	2.9.3
pest_generator	2.9.2	2.9.3
pest_meta	2.9.2	2.9.3

No dependencies left un-upgraded.

Verification

• cargo build --all-targets — ✅ passes
• cargo clippy --all-targets — ✅ passes (no warnings)
• cargo xfmt --check — ✅ passes (no formatting changes)
• cargo test — ✅ 19 tests pass