Add PythonDependencyFile trait for polymorphic dependency management

[Jenson3210]

Summary

• Introduces the PythonDependencyFile trait with implementations for PyProjectFile (pyproject.toml), RequirementsFile (requirements.txt), and PipfileFile (Pipfile), providing a polymorphic API for dependency operations: add, upgrade, remove, change, pin transitives, and search markers
• Refactors AddDependency, UpgradeDependencyVersion, RemoveDependency, ChangeDependency, and UpgradeTransitiveDependencyVersion to use the trait instead of duplicating TOML manipulation logic — removing ~800 lines of duplicated code
• All recipes now work on pyproject.toml, requirements.txt, and Pipfile files
• RequirementsFile supports scope-based filename filtering: scope=null matches all files, scope="" matches requirements.txt, scope="dev" matches requirements-dev.txt
• PipfileFile supports [packages] and [dev-packages] sections via scope parameter, including inline table dependencies (django = {version = ">=3.2", extras = ["postgres"]})
• Adds PipfileParser for parsing Pipfile and attaching PythonResolutionResult markers with PackageManager.Pipenv
• Package name normalization (PEP 503) is handled internally by the trait — callers don't need to pre-normalize

Test plan

• 41 trait unit tests (PythonDependencyFileTest) covering all trait methods, matcher, scope filtering, and static utilities
• 15 Pipfile trait unit tests (PipfileFileTest) covering matcher, upgrade, add, remove, change, and search markers
• All existing recipe tests pass (AddDependency, UpgradeDependencyVersion, UpgradeTransitiveDependencyVersion, RemoveDependency, ChangeDependency)
• New requirements.txt recipe integration tests for all 4 direct-dependency recipes
• New Pipfile recipe integration tests for all 5 recipes
• 126 total tests passing