[dt][caffe2] enable using smart exceptions in async nets (#34753)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34753
This improves support for exceptions and capturing stack traces in caffe2 async nets. We generally want to use exceptions everywhere we can in order to preserve stack information. It also makes the exception timestamp more accurate so multiple exceptions at the same time can be correctly ordered.
Test Plan: Updated the tests to use the new error semantics + adds a test to ensure the stack is correctly propagated through deferrable async scheduling.
Reviewed By: andrewwdye
Differential Revision: D20449887
fbshipit-source-id: 047fdf1bd52fd7c7c1f3fde77df9a27ed9e288e7
