[Backend Tester] Report delegation statistics

[GregoryComer]

Report total number of delegated and undelegated nodes and breakdown by operator count.

Important Note: This includes a placeholder change in EdgeProgramManager to preserve the original edge graph. This will be replaced with the edge graph from the ETRecord when it's available with to_edge_transform_and_lower. I'm keeping this PR in draft until then.

Example from CoreML add:

Test ID	Test Case	Backend	Delegated Nodes	Undelegated Nodes	Delegated Ops	Undelegated Ops
test_add_dtype_float32_coreml	test_add_dtype	coreml	1	0	{'aten::add.Tensor': 1}	{}
test_add_dtype_float32_coreml_static_int8	test_add_dtype	coreml	7	0	{'aten::add.Tensor': 1, 'quantized_decomposed::dequantize_per_tensor': 3, 'quantized_decomposed::quantize_per_tensor': 3}	{}

[GregoryComer]

Stack from ghstack (oldest at bottom):

• -> [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]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12846

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❌ 1 New Failure

As of commit 4719c90 with merge base 4fd2079 ():

NEW FAILURE - The following job has failed:

• pull / test-llava-runner-linux / linux-job (gh)
  test_llava_export

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[GregoryComer]

For reviewers, is there a better way to present the operator counts? Are there other delegation-related stats that we should include?