fix(db): parameterize sessionmaker with Session

[laipz8200]

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Summary

Fixes #30610.

Update the global session factory typing in api/core/db/session_factory.py to use sessionmaker[Session], preserving the inner Session type for consumers and improving type-checking accuracy without runtime changes. No dependencies required.

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @laipz8200, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the type safety and clarity within the session_factory.py module by refining the type annotations for sessionmaker. By explicitly specifying sessionmaker[Session], the changes ensure that static analysis tools can more accurately infer the type of database sessions being managed, thereby improving code maintainability and reducing the likelihood of type-related errors.

Highlights

• Type Annotation Improvement: The type annotation for the _session_maker variable has been updated from sessionmaker to sessionmaker[Session] to explicitly define the generic type.
• Function Return Type Update: The return type annotation for the get_session_maker function has been changed to sessionmaker[Session], providing more precise type information.
• Static Method Return Type Update: The return type annotation for the SessionFactory.get_session_maker static method has also been updated to sessionmaker[Session] for consistency and clarity.

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[gemini-code-assist]

Code Review

This pull request correctly improves the type annotations for sessionmaker to include the inner Session type, which enhances type safety and code clarity. The changes are consistent across the module. I've also included a suggestion to refactor the session factory logic to avoid using a global variable, which would improve the code's maintainability and testability by encapsulating the state within the SessionFactory class.