Upgrade the Rust toolchain to 1.99.1 (#61205)

## What changed

- Update the workspace, Bazel toolchain and lockfile, CI and release workflows, and Windows setup script from Rust `1.95.0` to `1.99.1`.
- Adapt Rust code to the updated toolchain and Clippy lints, including `try_update` for atomics, `as_chunks` for fixed-size slices, and targeted allowances for generated tonic services.
- Refresh the halfwidth sound mark rendering snapshot to use literal characters in debug output.

GitOrigin-RevId: 5852029f687436dc814c2bca68141ee1f4a67d49

codex-rs/agent-identity/src/lib.rs

@@ -565,7 +565,6 @@ fn signing_key_from_private_key_pkcs8_base64(private_key_pkcs8_base64: &str) ->
 
 #[cfg(test)]
 mod tests {
-    use base64::Engine as _;
     use ed25519_dalek::Signature;
     use ed25519_dalek::Verifier as _;
     use jsonwebtoken::EncodingKey;