Fix mutable default arguments and resource leaks (#44287)
* Fix mutable default arguments and resource leaks
Mutable defaults (shared state across calls):
- debug_utils.py: DebugUnderflowOverflow trace_batch_nums=[] -> None
- kernel_config.py: KernelConfig kernel_mapping={} -> None
- modeling_idefics.py: freeze_model/freeze_text_layers/freeze_vision_layers
module_exceptions=[] -> ()
- convert_usefulsensors_to_hf.py: _read_h5_weights weights={} -> None
(actively mutated via dict assignment)
Resource leaks (file handles not closed):
- processing_utils.py: open().read() in chat template loading -> context manager
- tokenization_myt5.py: json.load(open()) -> context manager
- cli/serve.py: config_path.open().read() -> context manager
* Revert file handle changes per review feedback
The open().read() patterns without variable assignment are
immediately unreachable and cleaned up by CPython's reference
counting GC, so context managers are unnecessary here.
Keeps the mutable default argument fixes which are real bugs.
