[ExecuTorch][Core AI][5/x] Enumerated input-shape support

[metascroy]

Adds enumerated input shapes. The partitioner resolves per input enumerations to export symbols, and preprocess substitutes them into each delegate boundary and attaches them via set_static_shape_config, letting a delegate carry several concrete shapes for a dynamic dim. Includes shape config tests.

[pytorch-bot]

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❌ 2 New Failures, 1 Unrelated Failure

As of commit 23e40da with merge base 161d9f9 ():

NEW FAILURES - The following jobs have failed:

• pull / test-llama-runner-qnn-linux (fp32, qnn_8a8w, qnn) / linux-job (gh)
  curl: (22) The requested URL returned error:
• Test WebGPU Backend / test-webgpu / test-backend-linux (webgpu, models) / linux-job (gh)
  curl: (22) The requested URL returned error:

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-models-linux (mv2, portable, linux.2xlarge) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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