Improve booru fav

[icceey]

This pull request introduces a restriction on the use of the fav (favorite count) filter for booru subscriptions, making it only available for Danbooru-based sites. The changes ensure users are notified with a clear message if they attempt to use the fav filter on unsupported engines, and this logic is both implemented in the code and covered by new tests.

Booru filter engine support and user feedback:

• Added a new method supports_fav_count to BooruEngineType, returning true only for Danbooru engines, to centralize the logic for favorite count support.
• Introduced the unsupported_fav_filter_message helper, which checks if a user tried to use the fav filter on a site that does not support it, and returns a user-friendly error message if so. This helper is now called in all relevant booru subscription command handlers before proceeding, ensuring consistent user feedback. [1] [2] [3] [4]

Testing:

• Added a unit test for unsupported_fav_filter_message to verify that it only returns an error message for unsupported engines and not for Danbooru.

Documentation:

• No documentation changes were made for this specific feature, but the logic is clearly encapsulated and tested.

Dependency management:

• Updated .github/dependabot.yml to ignore minor and patch updates for all dependencies, reducing noise from Dependabot for small version changes.