feat(animatable): add unanimatable view modifier

[Kyle-Ye]

Summary

• Add the private View.unanimatable() SPI.
• Add a shared example that compares animated and non-animated height changes, with the SwiftUI SPI declaration needed to run it against either implementation.

[tuist]

🛠️ Tuist Run Report 🛠️

Tests 🧪

Scheme	Status	Ran test modules	Commit
OpenSwiftUI	✅	7	e85b5ed8f

Builds 🔨

Scheme	Status	Duration	Commit
OpenSwiftUI	✅	42.4s	e85b5ed8f

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.12%. Comparing base (b881f2b) to head (8fbaf08).

Files with missing lines	Patch %	Lines
...nSwiftUICore/Animation/Animatable/Animatable.swift	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1097      +/-   ##
==========================================
- Coverage   33.56%   33.12%   -0.45%     
==========================================
  Files         797      803       +6     
  Lines       61897    63674    +1777     
==========================================
+ Hits        20774    21090     +316     
- Misses      41123    42584    +1461     

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