[Backend Tester] Clean up operator test logic

[GregoryComer]

Minor refactoring on the operator test logic - since we now have separate model tests, I've moved operator-test specific test helper logic into the operators directory and updated usages. I also updated discovery slightly to give nicer error messages when things don't import.

[GregoryComer]

Stack from ghstack (oldest at bottom):

• [Backend Tester] Add CSV report generation #12741
• [Backend Tester] [WIP] Add Qualcomm tester and register flow #12739
• [Backend Tester] Add Vulkan tester and register test flow #12738
• -> [Backend Tester] Clean up operator test logic #12736

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12736

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❌ 2 New Failures, 14 Pending

As of commit e2df06e with merge base 1af1d11 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t f162181b2e6bac62a4d56c66809671fe7ebbaa61633304be2fcc41376bfa3189 /exec failed with exit code 5
• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t ec2b722cff579d4afd9c2215fa87d4c6737ebf1e2279ca6313856f3e9674ffa7 /exec failed with exit code 5

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[digantdesai]

do you envision suite/<type>/__init__.py per suite as a "controller" for writing tests? How do you see enforcing some suite level characteristics then? like all suits do this or support that.

[GregoryComer]

do you envision suite/<type>/__init__.py per suite as a "controller" for writing tests? How do you see enforcing some suite level characteristics then? like all suits do this or support that.

It's a good point. As a follow-up, I'll refactor out the common logic from the model and operator tests.

[GregoryComer]

Unit test failures are pre-existing on main.