Modernize type annotations to Python 3.9+ style

[jssmith]

Summary

Update type annotations throughout the codebase to use Python 3.9+ built-in generics instead of typing module equivalents.

Changes needed

Replace deprecated typing imports with built-in types:

• List[X] → list[X]
• Dict[K, V] → dict[K, V]
• Set[X] → set[X]
• Tuple[X, Y] → tuple[X, Y]
• Optional[X] → X | None
• Union[X, Y] → X | Y
• Iterable, Generator → import from collections.abc

Files affected

• src/postgres_mcp/database_health/database_health.py
• src/postgres_mcp/index/index_opt_base.py
• src/postgres_mcp/index/presentation.py
• src/postgres_mcp/server.py
• src/postgres_mcp/sql/safe_sql.py
• tests/unit/index/test_dta_calc.py
• tests/unit/sql/test_sql_driver.py
• tests/utils.py

How to apply

Run:

uv run ruff check . --fix --unsafe-fixes
uv run ruff format .

Cleanup required

After applying fixes, remove the following lint.ignore rules from pyproject.toml:

# TODO: Remove these ignores when fixing #129 (code modernization)
lint.ignore = [
    "UP006",  # Use `list` instead of `List` for type annotations
    "UP035",  # Import from `collections.abc` instead of `typing`
    "UP045",  # Use `X | None` instead of `Optional[X]`
    "RUF059", # Unused unpacked variable
    "RUF100", # Unused noqa directive
]

Context

This was deferred during the dependency version bump (#130) to avoid breaking existing PRs with merge conflicts.