Reduce area of tiled API being wrapped

[tpoliaw]

• Remove derives from types that no longer need them
• Remove Links struct and associated fields
• Reduce visibility of fields where possible

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 51.00%. Comparing base (9e4e542) to head (80ecc53).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/model/node.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #92      +/-   ##
==========================================
- Coverage   52.64%   51.00%   -1.65%     
==========================================
  Files          13       13              
  Lines         585      600      +15     
==========================================
- Hits          308      306       -2     
- Misses        277      294      +17     

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