refactor: add PEP 484 type annotations across the codebase (#164)

[Chimankarparag]

Add comprehensive type hints to all core modules using Python 3.9+ compatible syntax (no 'from future import annotations').

• Annotate factory, operation, schema, version, utils, fetcher, reverter, transaction, expression_reflector modules
• Annotate table_builder, model_builder, relationship_builder, builder
• Annotate manager, unit_of_work, and init public API
• Annotate all plugins (activity, base, null_delete, property_mod_tracker, transaction_changes, transaction_meta)
• Use TYPE_CHECKING guards to prevent circular imports
• Fix pre-existing ruff warnings (FBT001, PERF401, A003)

[Chimankarparag]

The Test cases failed due an incompatible annotations in utils.py
Passed tests on python 3.9, DB = sqlite after the change was made.

[coveralls]

Coverage Report for CI Build 25801782794

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No base build found for commit 5fe88b1 on main.
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Coverage: 95.68%

Details

• Patch coverage: 34 uncovered changes across 16 files (286 of 320 lines covered, 89.38%).

Uncovered Changes

Top 10 Files by Coverage Impact	Changed	Covered	%
sqlalchemy_history/plugins/activity.py	19	9	47.37%
sqlalchemy_history/plugins/base.py	28	24	85.71%
sqlalchemy_history/plugins/transaction_changes.py	14	11	78.57%
sqlalchemy_history/factory.py	7	5	71.43%
sqlalchemy_history/operation.py	28	26	92.86%
sqlalchemy_history/plugins/property_mod_tracker.py	9	7	77.78%
sqlalchemy_history/utils.py	29	27	93.1%
sqlalchemy_history/init.py	4	3	75.0%
sqlalchemy_history/fetcher.py	20	19	95.0%
sqlalchemy_history/model_builder.py	16	15	93.75%

Coverage Regressions

Requires a base build to compare against. How to fix this →

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Coverage Stats

Relevant Lines:	5718
Covered Lines:	5471
Line Coverage:	95.68%
Coverage Strength:	9.51 hits per line

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💛 - Coveralls

[ashish16052]

will need to add sqlalchemy_history/py.typed marker and update the wheel to have

[tool.setuptools.package-data]
sqlalchemy_history = ["py.typed"]