chore: avoid implicit optional in type annotations of method

[bowenliang123]

Checklist:

Important

Please review the checklist below before submitting your pull request.

• Please open an issue before creating a PR or link to an existing issue
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Description

• to improve readability for misunderstanding the argument types, avoid implicit optional in type annotations of method, by applying RUF013 linting rule (https://docs.astral.sh/ruff/rules/implicit-optional/) , which is only altered when a non-optional method argument with a default value of None.
• All the changes are applied to the type annotation only.
• no behaviour changed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update, included: Dify Document
• Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement
• Dependency upgrade

Testing Instructions

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

[bowenliang123]

All the changes are applied and have been checked manually, including the imports and annotations. cc @laipz8200

[bowenliang123]

Hi @laipz8200 , may I raise a separate PR after this PR being merged , to resolve the comments you suggested which are not detected by the RUF013 rule and which of suggestions also indicates possible behaviour changes (e.g. removing unused parameters)?

[laipz8200]

Thank you for your hard work.

[bowenliang123]

Thanks for the detailed review. Will follow your comments later.