[tests] add generic size/type test for all ProcessGroups

[d4l3k]

We have quite a few different ProcessGroup implementations in https://github.com/pytorch-labs/torchft/blob/main/torchft/process_group.py

We want a standardized test helper to test world_size 1 behavior to ensure that all common/inputs have the right sizes/types.

Key requirements:

• We want to test all of the collectives supported by torchft.ProcessGroup https://github.com/pytorch-labs/torchft/blob/main/torchft/process_group.py#L88
• Should run realistic input types (float32, bfloat16?) and verify shapes/types of outputs
• We want to test the output behavior is correct both for Work.wait() and Work.get_future().
• Can call it multiple times with different configurations
• Optional: support world size >1

Add / update tests in https://github.com/pytorch-labs/torchft/blob/main/torchft/process_group_test.py

Example test:

def test_error_swallowing_process_group(self) -> None:
    pg = ErrorSwallowingProcessGroupWrapper(DummyProcessGroup(0, 1))

    self._test_pg(pg)

    pg.report_error(RuntimeException("some error"))

    # ensure that the default values after an error have the right shapes/types
    self._test_pg(pg)

[Krishn1412]

Hey @d4l3k , can I pick this up?

[d4l3k]

@Krishn1412 I had someone in mind already for this issue -- would you be interested in taking on #36 ?