feat: Add Actions cache limits for an organization

[NitinKumar004]

Fixes #4596

Adds the organization-level GitHub Actions cache limit endpoints to ActionsService, next to the existing cache usage methods in actions_cache.go:

• GetCacheRetentionLimitForOrg / SetCacheRetentionLimitForOrg (GET/PUT /organizations/{org}/actions/cache/retention-limit)
• GetCacheStorageLimitForOrg / SetCacheStorageLimitForOrg (GET/PUT /organizations/{org}/actions/cache/storage-limit)

The two new types, ActionsCacheRetentionLimit and ActionsCacheStorageLimit, are used for both the GET response and the PUT request body, since the OpenAPI schema is the same for both. The PUT endpoints return 204, so the setters return only (*Response, error), following UpdateArtifactAndLogRetentionPeriodInOrganization.

API docs: https://docs.github.com/rest/actions/cache#get-github-actions-cache-retention-limit-for-an-organization

Tested with unit tests for each method (happy path, bad options, request/do failure, 404 and invalid org), and script/generate.sh, script/fmt.sh, script/test.sh and script/lint.sh all pass locally. script/metadata.sh unused no longer lists these four operations.

Note: this change was prepared with AI assistance; I reviewed the code and ran the tests.

[google-cla]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.60%. Comparing base (93344bc) to head (5ccf153).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4597   +/-   ##
=======================================
  Coverage   98.60%   98.60%           
=======================================
  Files         198      198           
  Lines       18538    18566   +28     
=======================================
+ Hits        18279    18307   +28     
  Misses        259      259           

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[gmlewis]

@NitinKumar004 - once you resolve the CLA issue, we can move forward with this PR.

[NitinKumar004]

@gmlewis I've signed the Google CLA now, using the same email as the commit. Thanks for your patience!

[gmlewis]

Thank you, @NitinKumar004!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @Not-Dhananjay-Mishra

[gmlewis]

Just FYI - I just realized that we have not been terribly consistent in the use of integer types for fields representing GigaBytes, so I'm fine to leave this as-is.

$ rg _gb | grep int
github/actions_hosted_runners.go:       MemoryGB  int    `json:"memory_gb"`  // The available RAM for the machine spec. Example: 32
github/actions_hosted_runners.go:       StorageGB int    `json:"storage_gb"` // The available SSD storage for the machine spec. Example: 300
github/actions_hosted_runners.go:       SizeGB      *int64  `json:"size_gb"`      // Image size in GB. Example: 86
github/actions_hosted_runners.go:       SizeGB       int       `json:"size_gb"`
github/actions_hosted_runners.go:       SizeGB      int    `json:"size_gb"`