[Backend Tester] Report quantization and lowering times

[GregoryComer]

Track and report the time taken to quantize and lower in the backend test flow. Include this information in the generated report for each test case.

Example output (from testing add operator):

Test ID	Test Case	Backend	Flow	Result	Quantize Time (s)	Lowering Time (s)
test_add_dtype_float32_coreml	test_add_dtype	coreml	coreml	Success (Delegated)		0.69
test_add_dtype_float32_coreml_static_int8	test_add_dtype	coreml	coreml_static_int8	Success (Delegated)	8.73	0.88

[GregoryComer]

Stack from ghstack (oldest at bottom):

• [Backend Tester] Clean up a few test issues #13258
• [Backend Tester] Add portable test flow #13250
• [Backend Tester] Report PTE size #13249
• [Backend Tester] Report delegation statistics #12846
• -> [Backend Tester] Report quantization and lowering times #12838
• [Backend Tester] Add tensor error statistic reporting #12809
• [Backend Tester] Add CSV report generation #12741
• [Backend Tester] [WIP] Add Qualcomm tester and register flow #12739

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12838

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 3 New Failures, 1 Unrelated Failure

As of commit f260b50 with merge base 09d5255 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
  At least one of the pre-conditions you specified did not hold
• Lint / lintrunner / linux-job (gh)
  >>> Lint for backends/test/suite/runner.py:
• pull / test-moshi-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 6d1903f0c7b9893691836b7b5c0297e3b7128d95dbcd8ea30382726919307b48 /exec failed with exit code 1

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-openvino-linux / linux-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'quantized_decomposed' object has no attribute 'convert_element_type'

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[digantdesai]

LGTM