[4.x] Add more relation type annotations

[MrPunyapal]

This pull request adds improved PHPDoc type annotations to several Eloquent relationship methods, enhancing static analysis and developer experience. These changes clarify the expected return types for relationships, making the codebase easier to understand and work with.

Relationship method type annotations:

• Added a detailed return type annotation to the tenant method in the BelongsToTenant trait, specifying the related model and the current class.
• Added a detailed return type annotation to the domains method in the HasDomains trait, specifying the related model and the current class.
• Added a detailed return type annotation to the tenants method in the ResourceSyncing class, specifying the related model and the current class.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.92%. Comparing base (3c0e21b) to head (4fa82d3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1424   +/-   ##
=========================================
  Coverage     85.92%   85.92%           
  Complexity     1147     1147           
=========================================
  Files           184      184           
  Lines          3360     3360           
=========================================
  Hits           2887     2887           
  Misses          473      473           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[calebdw]

LGTM!

[stancl]

Thanks!