feat(database.eloquent): Add tenant child model functionality

[ollieread]

Add functionality to support tenant child models, from relationship handlers, to automating query context.

[codecov]

Codecov Report

Attention: Patch coverage is 98.19277% with 3 lines in your changes missing coverage. Please review.

Project coverage is 89.41%. Comparing base (b60b395) to head (d34b3dc).
Report is 2 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/TenancyOptions.php	75.00%	2 Missing ⚠️
src/Support/DefaultTenancy.php	90.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #32      +/-   ##
============================================
+ Coverage     85.68%   89.41%   +3.72%     
- Complexity      208      272      +64     
============================================
  Files            30       41      +11     
  Lines           573      737     +164     
============================================
+ Hits            491      659     +168     
+ Misses           82       78       -4     

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