Context manager open(file) as f fixes (#7289)

* Flask context manager `open()` fix

* Additional read context manager fixes

models/common.py

@@ -378,7 +378,8 @@ class DetectMultiBackend(nn.Module):
                     return x.prune(tf.nest.map_structure(ge, inputs), tf.nest.map_structure(ge, outputs))
 
                 gd = tf.Graph().as_graph_def()  # graph_def
-                gd.ParseFromString(open(w, 'rb').read())
+                with open(w, 'rb') as f:
+                    gd.ParseFromString(f.read())
                 frozen_func = wrap_frozen_graph(gd, inputs="x:0", outputs="Identity:0")
             elif tflite or edgetpu:  # https://www.tensorflow.org/lite/guide/python#install_tensorflow_lite_for_python
                 try:  # https://coral.ai/docs/edgetpu/tflite-python/#update-existing-tf-lite-code-for-the-edge-tpu