trunk/23341ddcfe7cc4813eb7ef760847d9b786336e1e: [dynamo] Restore autocast state between tests in TestCase (#195662)

发生了什么

Fixes #195487 . torch._dynamo.test_case.TestCase.setUp / tearDown already snapshots torch.is_grad_enabled() and restores it (with a warning) in tearDown if a test left it changed, but has no equivalent for autocast. All four pieces of autocast state -- enabled, dtype, cache_enabled, and the nesting counter -- survive past the end of a test into whichever test runs next. A test that leaks this state (e.g. by calling…

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