[Test] Refactor test_optim to improve test reuse and add `HardwareClassification` labels (#192741)

Change | Detail
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Remove onlyCPU import | Line 28 — no longer needed
Add HardwareClassification import | In common_utils block (alphabetical)
Add hw_classification | HardwareClassification.ACCELERATOR on TestOptimRenewed
Remove @onlyCPU × 2 | test_optim_infos_do_not_specify_global_cliquey_kwargs (metadata inspection) and test_step_with_empty_param_group (device-agnostic)
Enlarge @onlyCUDA → @onlyAccelerator | test_defaults_changed_to_foreach (mock-based, no Category C API)

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Generated by my agent
Pull Request resolved: https://github.com/pytorch/pytorch/pull/192741
Approved by: https://github.com/can-gaa-hou, https://github.com/fffrog, https://github.com/janeyx99