coreml : skip model load in convert-whisper-to-coreml.py

This commit adds the `skip_model_load` argument to the `convert_encoder`
and `convert_decoder` functions in the `convert-whisper-to-coreml.py`
file.

The motivation for this is that this is only needed if one intends to
perform inference on the model after conversion. In this case it also
seem to avoid an issue with larger models where the following error is
throws:
```console
Running MIL backend_neuralnetwork pipeline: 100%|█████████| 9/9 [00:00<00:00, 35.44 passes/s]
Translating MIL ==> NeuralNetwork Ops: 100%|███████████| 5641/5641 [03:31<00:00, 26.65 ops/s]
Traceback (most recent call last):
  File "/Users/danbev/work/ai/whisper-work/models/convert-whisper-to-coreml.py", line 322, in <module>
    encoder = convert_encoder(hparams, encoder, quantize=args.quantize)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danbev/work/ai/whisper-work/models/convert-whisper-to-coreml.py", line 255, in convert_encoder
    model = ct.convert(
            ^^^^^^^^^^^
  File "/Users/danbev/work/ai/whisper-work/venv/lib/python3.11/site-packages/coremltools/converters/_converters_entry.py", line 635, in convert
    mlmodel = mil_convert(
              ^^^^^^^^^^^^
  File "/Users/danbev/work/ai/whisper-work/venv/lib/python3.11/site-packages/coremltools/converters/mil/converter.py", line 186, in mil_convert
    return _mil_convert(
           ^^^^^^^^^^^^^
  File "/Users/danbev/work/ai/whisper-work/venv/lib/python3.11/site-packages/coremltools/converters/mil/converter.py", line 245, in _mil_convert
    return modelClass(
           ^^^^^^^^^^^
  File "/Users/danbev/work/ai/whisper-work/venv/lib/python3.11/site-packages/coremltools/models/model.py", line 489, in __init__
    self.__proxy__, self._spec, self._framework_error = self._get_proxy_and_spec(
                                                        ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/danbev/work/ai/whisper-work/venv/lib/python3.11/site-packages/coremltools/models/model.py", line 550, in _get_proxy_and_spec
    _MLModelProxy(
ValueError: basic_string
```

Refs: #3012

Author: danbev

models/convert-whisper-to-coreml.py

@@ -257,7 +257,8 @@ def convert_encoder(hparams, model, quantize=False):
         convert_to="neuralnetwork",
         inputs=[ct.TensorType(name="logmel_data", shape=input_shape)],
         outputs=[ct.TensorType(name="output")],
-        compute_units=ct.ComputeUnit.ALL
+        compute_units=ct.ComputeUnit.ALL,
+        skip_model_load=True,
     )
 
     if quantize:
@@ -282,7 +283,8 @@ def convert_decoder(hparams, model, quantize=False):
         inputs=[
             ct.TensorType(name="token_data", shape=tokens_shape, dtype=int),
             ct.TensorType(name="audio_data", shape=audio_shape)
-        ]
+        ],
+        skip_model_load=True,
     )
 
     if quantize: