Add Drupal 11 compatibility while retaining Drupal 10.3 support

Problem/Motivation

Entity Activity 2.0.0-beta1 supports Drupal 9.4 and Drupal 10, but the 2.x development line is intended for Drupal 10 and Drupal 11 only. Drupal 9 support should be removed, Drupal 10.3 should become the minimum supported core version, and Drupal 11 must be continuously tested without weakening Drupal 10 compatibility.

The current GitLab CI configuration disables the current-major lane and tests only the previous-major lane. It therefore does not prove Drupal 11 compatibility or pin the Drupal 10.3 minimum.

The existing PaCSON compatibility patch has been reviewed. Its substantive API fixes are already present in 2.x; any remaining differences must be assessed individually rather than applying the aggregate patch wholesale.

Proposed resolution

1. Change every module and test-module declaration to core_version_requirement: ^10.3 || ^11.
2. Resolve Drupal 11 API and runtime incompatibilities while retaining Drupal 10.3 compatibility.
3. Enable the official DrupalCI current-major lane for Drupal 11.
4. Add an explicit minimum-version Drupal 10.3 lane; do not rely only on the latest Drupal 10 release.
5. Run the existing PHPUnit suite against both Drupal 10.3 and Drupal 11, retaining the document-root and /web subdirectory coverage.
6. Keep the production-PHP line-coverage threshold at 80% or higher and keep all lint/static-analysis jobs blocking.
7. Publish the completed work in 2.0.0-beta2. The immutable beta1 package must continue to state that Drupal 11 is not included.

Remaining tasks

• [x] All *.info.yml files declare exactly ^10.3 || ^11.
• [x] Composer installation succeeds on the pinned Drupal 10.3 minimum and current Drupal 11.
• [x] PHPUnit passes on Drupal 10.3 and Drupal 11.
• [x] Functional coverage passes in both document-root and /web subdirectory installations.
• [x] Production PHP line coverage remains at least 80%.
• [x] CSpell, ESLint, PHPCS, PHPStan, Stylelint, and composer-lint remain green and blocking.
• [x] Upgrade Status/static analysis reports no unresolved Drupal 11 compatibility blockers.
• [x] A successful merged-results pipeline is linked before the issue moves to Needs review.

User interface changes

None expected.

API changes

The supported core API range changes from Drupal 9.4/10 to Drupal 10.3/11. Any implementation-level API changes required for Drupal 11 must preserve the module's existing public behaviour and be documented in the merge request.

Data model changes

None expected.