Add GraphValue and GraphMutation implementation

[Kyle-Ye]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 84 lines in your changes are missing coverage. Please review.

Project coverage is 17.80%. Comparing base (abbf4d6) to head (a189520).

Files	Patch %	Lines
Sources/OpenSwiftUI/Core/Graph/GraphHost.swift	0.00%	50 Missing ⚠️
Sources/OpenSwiftUI/Core/Graph/GraphMutation.swift	0.00%	13 Missing ⚠️
Sources/OpenSwiftUI/Core/Graph/GraphValue.swift	0.00%	10 Missing ⚠️
Sources/OpenSwiftUI/Core/Graph/GraphInputs.swift	0.00%	9 Missing ⚠️
.../Environment/Internal/TODO/CachedEnvironment.swift	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
- Coverage   18.22%   17.80%   -0.42%     
==========================================
  Files         158      160       +2     
  Lines        2947     3016      +69     
==========================================
  Hits          537      537              
- Misses       2410     2479      +69     

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