Preserve metadata for `MutableMapping` and `MutableSequence` in `pin_memory` and `collate_fn` (#120553)
For the user-defined `Mapping` type, it may contain some metadata (e.g., pytorch/tensordict#679, https://github.com/pytorch/pytorch/pull/120195#issue-2141716712). Simply use `type(mapping)({k: v for k, v in mapping.items()})` do not take this metadata into account. This PR uses `copy.copy(mapping)` to create a clone of the original collection and iteratively updates the elements in the cloned collection. This preserves the metadata in the original collection via `copy.copy(...)` rather than relying on the `__init__` method in the user-defined classes.
Reference:
- pytorch/tensordict#679
- #120195
Closes #120195
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120553
Approved by: https://github.com/vmoens
