ckeditor_tweetthis 3.1.0

Drupal 12 compatibility release.

- Drupal 12 support: core_version_requirement ^10.3 || ^11 || ^12.
- Fixed: CKEditor 5 editor failed to load on Drupal 12 when the Tweet button was in the toolbar (Drupal 12 uses the CKEditor 5 UMD build). The plugin now works on Drupal 10.3, 11 and 12.
- hook_page_attachments() moved to an OOP Hook class with dependency injection and proper cache tags (no more full cache flush when saving settings).
- Added config schema and default configuration.
- Coding standards fixes (Drupal, DrupalPractice).
- Removed obsolete core/jquery.once library dependency.
- Dropped Drupal 9 and Drupal 10.0–10.2 support.

Issue: #3596296