perf: add teardown logic for watch (#980)

When the observable has complete or errored. The watch should be closed.

Author: alan-agius4

src/lib/file/file-watcher.ts

@@ -33,5 +33,6 @@ export function createFileWatch(
 
   return Observable.create(observer => {
     watch.on('all', (event: FileWatchEvent, filePath: string) => handleFileChange(event, filePath, observer));
+    return () => watch.close();
   });
 }