Format Rust workspace and enforce rustfmt in CI - #105

Summary

• apply cargo fmt --all to the remaining unformatted Rust workspace files
• add a fast format CI job that runs cargo fmt --all -- --check
• make the main test job depend on formatting and document the enforced command

The Rust source changes in this PR are formatting-only.

Validation

• cargo fmt --all -- --check
• cargo test -p dynwinrt --quiet (247 passed, 1 ignored)
• cargo check -p static-bench-rust --quiet
• git diff --check