[eas-build-job] Add local action schema

[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.

How

Introduce the action config schema in @expo/eas-build-job, the single source of truth for the shape of an action.yml file. No runtime behavior changes yet.

Added:

• ActionConfigZ / ActionConfig: Zod schema and type for action.yml (inputs, outputs, runs.steps)
• validateActionConfig: validates a raw action config against the schema

Test Plan

Added unit tests for validateActionConfig.

[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
• [steps] Add local action discovery utilities #3956
• [eas-build-job] Add local action schema #3928 👈 (View in Graphite)
• main

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.28%. Comparing base (a848411) to head (06676aa).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3928      +/-   ##
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+ Coverage   59.28%   59.28%   +0.01%     
==========================================
  Files         935      936       +1     
  Lines       41093    41101       +8     
  Branches     8660     8660              
==========================================
+ Hits        24356    24364       +8     
  Misses      16643    16643              
  Partials       94       94              

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[github-actions]

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[sjchmiela]

current steps thing should require using: composite maybe?

[sswrk]

Are we expecting to add more options apart from composite? I'm not sure if there's much value in expecting explicit using: composite vs making it implicit and documenting it.

[sjchmiela]

do we want to call these actions (straight off of GitHub Actions) or functions (borrowing off https://docs.expo.dev/custom-builds/schema/#functions)?

[sjchmiela]

might be more of a product decision (cc @jonsamp -- those are the reusable… Things from https://linear.app/expo/project/user-functions-reusable-steps-reusable-jobs-reusable-workflows-394b14f18567/overview)

[sswrk]

I'm liking "functions" more and more, this name clearly communicates that it's about reusability, composability, input/output, encapsulation etc. "Action" feels like something more heavy-weight, something that does something significant, which won't always be the case here. Also, in the docs here https://docs.expo.dev/eas/workflows/syntax/#jobsjob_idstepsstepuses we're referencing "a set of built-in reusable functions"

[github-actions]

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