fix(trainer): add missing type hints to LocalJob class

[codebyNJ]

What this PR does / why we need it:

Adds comprehensive type hints and improves documentation for the LocalJob class in the localprocess backend. The class was missing type annotations on __init__ parameters (name, execution_dir, env, dependencies), all properties (stdout, success, status, returncode, creation_time, completion_time), and methods (run, cancel, stream_logs). Docstrings also had redundant type info in Args sections instead of relying on the signature annotations.

This aligns the code with the project's AGENTS.md guidelines:

"All Python code MUST include type hints and return types."

Changes:

• Add type hints to all __init__ parameters (notably name: str, execution_dir: str | None, env: dict[str, str] | None, dependencies: list[LocalJob] | None)
• Add return type annotations to all properties and methods
• Fix tuple[str] to correct tuple[str, ...] for variadic tuple type
• Update docstrings to Google style without redundant type annotations
• Add from __future__ import annotations for forward reference support
• Import Iterator from collections.abc for stream_logs return type

Checklist:

• Docs included if any changes are user facing
• Tests pass (18/18 in localprocess/backend_test.py)
• ruff format --check passes
• Follows Conventional Commits format

[google-oss-prow]

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[github-actions]

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[Copilot]

Pull request overview

Adds missing type annotations and updates docstrings for LocalJob in the localprocess backend to better align with the repo’s typed-Python guidelines and improve readability/IDE support.

Changes:

• Added from __future__ import annotations and updated imports to support forward references and iterator typing.
• Added/updated type hints for LocalJob.__init__, properties, and methods (including fixing tuple[str] to tuple[str, ...]).
• Refreshed docstrings to avoid redundant type info and better describe behavior.