fix: annotate context managers with Generator for ty 0.0.85

[lesnik512]

Summary

Closes #68

ty 0.0.85 bundles a typeshed that deprecates the contextmanager overload for functions annotated -> Iterator[T]. ty check reported this as two warnings in modern_di_typer/main.py, which failed the scheduled lint-ci run.

The new annotations come from collections.abc. typing.Generator needs all three type arguments before Python 3.13, so typing.Generator[Container] would fail at runtime on 3.11 and 3.12.

Changes

• _build_command_container and action_scope now return collections.abc.Generator[Container] instead of typing.Iterator[Container].

Checklist

• Lint and format pass (ruff)
• Type check passes (ty)
• Tests pass and new behavior is covered
• Build succeeds (uv build) if packaging or build config changed
• Repo metadata stays consistent across the three surfaces (GitHub description, pyproject description, profile blurb) if this touches packaging