Fix Self import for Python 3.10 compatibility

[tauhid621]

Summary

• typing.Self was introduced in Python 3.11, causing ImportError on Python 3.10
• Uses a version-guarded import to fall back to typing_extensions.Self on Python < 3.11
• Fixes regression introduced in [TIDY-FIRST] Add typing graph/manifest.py and graph/nodes.py #12795

Test plan

• Verify import succeeds on Python 3.10
• Verify import succeeds on Python 3.11+
• Run existing test suite

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[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.40%. Comparing base (1c98ad2) to head (e18d0e4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12809      +/-   ##
==========================================
- Coverage   91.41%   91.40%   -0.02%     
==========================================
  Files         203      203              
  Lines       25875    25879       +4     
==========================================
+ Hits        23654    23655       +1     
- Misses       2221     2224       +3     

Flag	Coverage Δ
integration	88.26% <75.00%> (-0.02%)	⬇️
unit	65.52% <75.00%> (+<0.01%)	⬆️

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Components	Coverage Δ
Unit Tests	65.52% <75.00%> (+<0.01%)	⬆️
Integration Tests	88.26% <75.00%> (-0.02%)	⬇️

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