feat(actions): add go-cache composite action with S3 support

README.md

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+# actions-go
+
+Reusable Gitea Actions for Go projects.
+
+## actions/go-cache
+
+Composite action that installs Go, installs `tailscale/go-cache-plugin`, and configures Go's native `GOCACHEPROG` to cache Go build and test artifacts in an S3-compatible backend.
+
+This action avoids the need to tar/untar huge build directories manually and leverages standard S3 object storage for fast, reliable caching.
+
+### S3 usage
+
+Create an S3 bucket for your Go build cache, then pass S3 settings as inputs and credentials as normal workflow environment variables or secrets.
+
+For ease of use and compatibility with `actions-rust`, the action automatically maps `SCCACHE_AWS_ACCESS_KEY_ID` and `SCCACHE_AWS_SECRET_ACCESS_KEY` to standard AWS environment variables if they are provided.
+
+```yaml
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Go + S3 Caching
+        uses: https://git.ericxliu.me/eric/actions-go/.gitea/actions/go-cache@main
+        with:
+          go-version: '1.24'
+          s3-bucket: my-go-cache-bucket
+          s3-endpoint: https://s3.example.com
+          s3-path-style: "true"
+        env:
+          SCCACHE_AWS_ACCESS_KEY_ID: ${{ secrets.SCCACHE_AWS_ACCESS_KEY_ID }}
+          SCCACHE_AWS_SECRET_ACCESS_KEY: ${{ secrets.SCCACHE_AWS_SECRET_ACCESS_KEY }}
+          AWS_REGION: auto
+
+      - run: go test -v ./...
+```
+
+### Local usage
+
+Omit `s3-bucket` to fall back to the default `setup-go` action's local caching behavior:
+
+```yaml
+- name: Setup Go (local cache)
+  uses: https://git.ericxliu.me/eric/actions-go/.gitea/actions/go-cache@main
+  with:
+    go-version: '1.24'
+```
+
+### Inputs
+
+- `go-version`: Go version to install. Defaults to `stable`.
+- `cache`: Set to `"false"` to opt-out of all caching setup.
+- `go-cache-plugin-version`: Specific version tag or `latest` of the cache plugin. Defaults to `latest`.
+- `s3-bucket`: S3 bucket name. Empty means local caching only.
+- `s3-endpoint`: Optional S3-compatible endpoint URL (e.g., self-hosted MinIO or Ceph).
+- `s3-path-style`: Set to `"true"` for endpoints requiring path-style addressing (e.g., MinIO).
+- `cache-dir`: Local cache directory for caching. Defaults to `~/.cache/go-cache`.