Fix BelongsToMorphedLoader

[roxblnfk]

🔍 What was changed

Refactor BelongsToMorphedLoader that now uses explicit mapping, respects scopes and hierarchy.

📝 Checklist

• Closes 🐛 BelongsToMorphedLoader doesn't respect Scopes and mapping #540
• How was this tested:
  • Tested manually
  • Unit tests added

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.64%. Comparing base (8ac5a6e) to head (36b0f11).
⚠️ Report is 6 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...c/Select/Loader/Morphed/BelongsToMorphedLoader.php	91.66%	3 Missing ⚠️
src/Select/Traits/ColumnsTrait.php	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x     #541      +/-   ##
============================================
+ Coverage     91.42%   91.64%   +0.21%     
+ Complexity     1925     1920       -5     
============================================
  Files           123      123              
  Lines          4947     4945       -2     
============================================
+ Hits           4523     4532       +9     
+ Misses          424      413      -11     

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