chore: refactor site handler to take cache dir (#21918)

relates to: https://github.com/coder/internal/issues/1300

Refactors the options to the site handler to take the cache directory, rather than expecting the caller to call `ExtractOrReadBinFS` and pass the results.

This is important in this stack because we need direct access to the cache directory for compressed file caching.

site/bin.go

@@ -89,11 +89,15 @@ func (h *binHandler) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
 	http.FileServer(h.binFS).ServeHTTP(rw, r)
 }
 
-func newBinHandler(options *Options) *binHandler {
-	return &binHandler{
-		binFS:         options.BinFS,
-		metadataCache: newBinMetadataCache(options.BinFS, options.BinHashes),
+func newBinHandler(options *Options) (*binHandler, error) {
+	binFS, binHashes, err := ExtractOrReadBinFS(options.CacheDir, options.SiteFS)
+	if err != nil {
+		return nil, xerrors.Errorf("extract or read bin filesystem: %w", err)
 	}
+	return &binHandler{
+		binFS:         binFS,
+		metadataCache: newBinMetadataCache(binFS, binHashes),
+	}, nil
 }
 
 // ExtractOrReadBinFS checks the provided fs for compressed coder binaries and