Add explicit Gym container selection and pod scheme guard

[sjchmiela]

Summary

• ensure fastlane resolves an explicit workspace/project before generating Gymfiles, via a deterministic container helper
• guard both eas-cli and build-tools against Pod shared schemes that share the app scheme name with user-facing guidance on remediation
• cover new helpers with unit tests for Gymfile output and collision detection

Testing

• Not run (not requested)

[github-actions]

Subscribed to pull request

File Patterns	Mentions
**/*	@douglowder

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[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 52.41%. Comparing base (2655482) to head (d908db1).

Files with missing lines	Patch %	Lines
packages/eas-cli/src/project/ios/scheme.ts	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3407      +/-   ##
==========================================
+ Coverage   52.39%   52.41%   +0.02%     
==========================================
  Files         803      804       +1     
  Lines       33445    33461      +16     
  Branches     6970     6972       +2     
==========================================
+ Hits        17521    17536      +15     
- Misses      15842    15843       +1     
  Partials       82       82              

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[github-actions]

⏩ The changelog entry check has been skipped since the "no changelog" label is present.