Add crate-ci/typos spell checker to the project for automatic spell checking:
- Add _typos.toml configuration in .github/ (next to golangci config)
- Exclude generated protobuf files (*.pb.go, *.proto, etc.)
- Add typos job to GitHub Actions linters workflow
- Add lint-typos and lint-typos-changed targets to Makefile
- lint-typos-changed checks only files changed from main (fast for local dev)
- Integrate lint-typos-changed into main lint target for faster local runs
- Document inline ignore directives and --file-list usage in config

The spell checker will run in CI on all files, while local make lint
will only check changed files for better performance.