Restore keys by using the prefix

[breezewish]

Description

Hi, thanks for the cool action! This PR attempts to keep behavior of restoring keys by "prefix" instead of exact match (which is exactly the behavior of actions/cache). It could be useful in fallback scenarios.

Motivation and Context

For example:

- uses: actions/cache@v4
  with:
    path: |
      ~/.cache/go-build
      ~/go/pkg/mod
    key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
    restore-keys: |
      ${{ runner.os }}-go-

Suppose that our hash was updated from aaaaaa to bbbbbb, with cache of aaaaaa is available.

Previously actions/cache would first try to restore with keys Linux-go-bbbbbb and then fallback to latest cache with key Linux-go-<any>, which becomes a successful lookup of Linux-go-aaaaaa. So the cache is hit, and try to utilized as much as possible.

In gcs-cache, however, cache will be missed totally because there is no key Linux-go-bbbbbb and Linux-go-.

How Has This Been Tested?

I'm also wondering how this could be tested automatically! Could you give me some advice? Currently I'm testing it manually by applying it in my own workflow.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
  Considered as a bug fix because it now follows the actions/cache behavior.
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (add or update README or docs)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[danySam]

Hey @breezewish, thank you so much for this PR! The prefix-based lookup using getFiles is exactly the right approach to match actions/cache behaviour. Really appreciate you taking the time to implement this.

Sorry for taking so long to get around to merging this; it's been sitting way too long, and your fix is solid.

I've added a couple of commits on top of your work:

• Fixed the cache-hit output (it was always returning false because restoreFromGCS was returning the GCS path instead of the cache key). Now uses a { cacheKey, gcsPath } return type so the key comparison works correctly.
• Added a GCS mock and test suite covering exact match, prefix match, latest-file selection, and lookup-only scenarios.
• Rebuilt the dist/ bundles.

Tested this in production and everything works as expected — prefix matching, cache-hit: true on exact match, and save correctly skipped on cache hit.

Thanks again for the contribution! 🎉