Metal backend: Add INT32 and BOOL dtype support

[manuelcandales]

AOTI-generated code creates int32 tensors for topk indexing and bool
tensors for attention masks. Add both to the SupportedDTypes enum and
validation function.

Authored with Claude.

[manuelcandales]

Stack from ghstack (oldest at bottom):

• Qwen 3.5 MoE: Add Metal build target #18881
• Qwen 3.5 MoE: Add --backend metal export path #18880
• Qwen 3.5 MoE: Add Metal source transformations #18879
• Metal backend: Add gated delta rule kernel for linear attention #18878
• Metal backend: Add gather_qmv kernel for MoE expert-indexed quantized matmul #18877
• Metal backend: Add topk fallback kernel via MPSGraph #18876
• Metal backend: Add SDPA head_dim=256 support #18875
• -> Metal backend: Add INT32 and BOOL dtype support #18874

[pytorch-bot]

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❌ 2 New Failures, 3 Unrelated Failures

As of commit e7a7acc with merge base 5707e2a ():

NEW FAILURES - The following jobs have failed:

• Apple / test-demo-ios / mobile-job (ios) (gh)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.
• pull / android / run-emulator (gh)
  The process '/usr/local/lib/android/sdk/platform-tools/adb' failed with exit code 224

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

• Test XNNPACK Backend / test-xnnpack / package-golden-artifacts (gh) (detected as infra flaky with no log or failing log classifier)

BROKEN TRUNK - The following jobs failed but was present on the merge base:

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

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[Copilot]

Pull request overview

This PR updates the Apple Metal runtime shims’ dtype allowlist so AOTI-generated models can use int32 tensors (e.g., topk indices) and bool tensors (e.g., attention masks) without failing dtype validation.

Changes:

• Add INT32 and BOOL entries to the Metal backend SupportedDTypes enum.
• Extend is_dtype_supported_in_et_metal() to accept INT32 and BOOL.
• Simplify the validate_dtype() error log message.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
backends/apple/metal/runtime/shims/utils.h	Adds INT32 and BOOL to the supported dtype enum.
backends/apple/metal/runtime/shims/utils.cpp	Allows INT32/BOOL in dtype validation and updates the unsupported-dtype log message.

---

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[Copilot]

The updated log message in validate_dtype regresses debuggability vs the previous version: it no longer indicates which dtype codes are supported. Please either restore the supported-dtypes list (updated to include INT32 and BOOL) or log it in a way that stays in sync with is_dtype_supported_in_et_metal (e.g., via a single source of truth).

Suggested change

	"Unsupported dtype: %d",
	dtype);
	"Unsupported dtype: %d. Supported dtype codes: [%d, %d, %d, %d, %d, %d]",
	dtype,
	static_cast<int32_t>(SupportedDTypes::UINT8),
	static_cast<int32_t>(SupportedDTypes::INT32),
	static_cast<int32_t>(SupportedDTypes::INT64),
	static_cast<int32_t>(SupportedDTypes::FLOAT32),
	static_cast<int32_t>(SupportedDTypes::BOOL),
	static_cast<int32_t>(SupportedDTypes::BFLOAT16));