* Add --update-crate flag to update a single vendored tool crate
Adds a --update-crate=<name>@<version> option to tools/crates/update.py
that updates one crate in-place without running cargo vendor. It downloads
the tarball directly from crates.io, replaces the vendor directory, patches
Cargo.lock, and regenerates .cargo-checksum.json. This avoids collateral
version bumps from a full re-vendor and is useful for targeted security
advisory fixes.
Exposes the flag via `npm run update_brave_tools_crates -- --update-crate=`.