feat: Migrate type checking from mypy to ty

[awinml]

Summary

Migrate the project type checker from mypy to ty and apply the source updates required for ty compatibility.

Changes

• Replaced mypy with ty in pyproject.toml
• Removed [tool.mypy] configuration
• Added [tool.ty] configuration and overrides
• Updated Makefile so make lint-typing runs uv run ty check src/ tests
• Replaced the pre-commit mypy hook with a local ty hook
• Updated pre-commit CI skip config from mypy to ty
• Updated RAG pipeline files for ty compatibility:
  • removed explicit Dataset annotations from load_dataset(...) calls
  • removed now-unused Dataset imports
• Updated type-ignore comments for ty compatibility
• Removed stale cached-decorator # type: ignore comments where ty no longer requires them
• Updated contributor documentation to reference ty

Checklist

• Code follows project style (make lint-check)
• Type annotations pass (make lint-typing)
• No typos (make lint-typos)
• No new security issues (make security-bandit)
• Dependency vulnerabilities checked (make security-audit)
• Pre-commit hooks pass (uv run pre-commit run --all-files)

[gemini-code-assist]

Code Review

This pull request replaces mypy with ty as the project's type checker, updates configuration files, and expands the CONTRIBUTING.md documentation with development commands and contribution guidelines. The reviewer feedback highlights three main areas for improvement: first, the configuration in pyproject.toml broadly ignores core type-checking rules, which significantly reduces the utility of static analysis; second, the documentation incorrectly describes ty as Astral's Rust-based type checker (which is actually redknot); and third, a dictionary lookup in fixed_schema_enricher.py can be simplified using .get() to avoid a double lookup and eliminate an inline type ignore.