[eas-build-job] Add local action schema and utils

[sswrk]

Why

First step toward local actions for EAS Workflows: reusable step groups referenced via uses: in .eas/workflows/*.yml, similar to GitHub Actions.

This PR adds the shared contract in @expo/eas-build-job so all consumers agree on action config shape and local action references.

How

Introduce the action config schema and shared utilities in @expo/eas-build-job: validation, local reference parsing, transitive catalog building with cycle detection, and safe path resolution within the EAS project root. No runtime behavior changes yet.

Added utilities:

• ActionConfigZ / validateActionConfig: Zod schema and validator for action.yml
• parseActionReference, normalizeActionReference, isActionReference, isLocalActionReference: distinguish ./ local actions from built-in uses: values like eas/build
• collectActionReferencesFromSteps: extract local action refs from a step list
• buildActionCatalogFromStepsAsync: transitively load actions via injected ActionLoader, with cycle detection
• resolveLocalActionPath: resolve a local uses: ref to an absolute path within the EAS project root (any ./-prefixed location, not just .eas/actions/)
• getActionNotFoundError, getActionOutsideProjectError, getActionCycleError, getWorkflowLocalActionsMissingError, getWorkflowLocalActionsCycleError: shared user-facing error copy

Test Plan

Added unit tests.

[linear-code]

ENG-22387

[sswrk]

• [eas-cli] Validate local actions in workflow files #3931
• [build-tools] Load local action catalog at build runtime #3930
• [steps] Expand local actions at parse time #3929
• [eas-build-job] Add local action schema and utils #3928 👈 (View in Graphite)
• main

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[codecov]

Codecov Report

❌ Patch coverage is 89.53488% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.34%. Comparing base (a848411) to head (d1bbabd).

Files with missing lines	Patch %	Lines
packages/eas-build-job/src/action.ts	89.42%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3928      +/-   ##
==========================================
+ Coverage   59.28%   59.34%   +0.07%     
==========================================
  Files         935      936       +1     
  Lines       41093    41179      +86     
  Branches     8660     8677      +17     
==========================================
+ Hits        24356    24433      +77     
- Misses      16643    16652       +9     
  Partials       94       94              

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[github-actions]

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