feat: Add optional caching to skip repeated Tailscale downloads and builds

This commit introduces a new `use-cache` input to the Tailscale GitHub Action. When set to `true`, the action will attempt to restore/install Tailscale binaries from a GitHub Actions cache, rather than always downloading or rebuilding them. If the cache is a hit, the download/build steps are
skipped, reducing network flakes and speeding up workflows. The default `false` preserves the
original behavior, ensuring full backward compatibility.