fix: improve NewObjectReader implementation for careful cleanup usage (#12199)

cleanup functions should never be cleaned before the reader is
instantiated, this type of design leads to situations where order
of lockers and places for them to use becomes confusing.

Allow WithCleanupFuncs() if the caller wishes to add cleanupFns
to be run upon close() or an error during initialization of the
reader.

Also make sure streams are closed before we unlock the resources,
this allows for ordered cleanup of resources.

cmd/disk-cache-backend.go

@@ -936,16 +936,16 @@ func (c *diskCache) Get(ctx context.Context, bucket, object string, rs *HTTPRang
 		objInfo.Size = rngInfo.Size
 		rs = nil
 	}
-	var nsUnlocker = func() {}
+
 	// For a directory, we need to send an reader that returns no bytes.
 	if HasSuffix(object, SlashSeparator) {
 		// The lock taken above is released when
 		// objReader.Close() is called by the caller.
-		gr, gerr := NewGetObjectReaderFromReader(bytes.NewBuffer(nil), objInfo, opts, nsUnlocker)
+		gr, gerr := NewGetObjectReaderFromReader(bytes.NewBuffer(nil), objInfo, opts)
 		return gr, numHits, gerr
 	}
 
-	fn, off, length, nErr := NewGetObjectReader(rs, objInfo, opts, nsUnlocker)
+	fn, off, length, nErr := NewGetObjectReader(rs, objInfo, opts)
 	if nErr != nil {
 		return nil, numHits, nErr
 	}