Update usages of DataLoader::SegmentInfo::Type::External

[pytorchbot]

This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #15195 by @lucylq
^ Please use this as the source of truth for the PR details, comments, and reviews
ghstack PR base: https://github.com/pytorch/executorch/tree/gh/lucylq/120/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/lucylq/120/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/lucylq/120/orig
Differential Revision: D83671426
@diff-train-skip-merge

[pytorch-bot]

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❌ 2 New Failures, 4 Unrelated Failures

As of commit 11ae625 with merge base f8e199c ():

NEW FAILURES - The following jobs have failed:

• Test CUDA Builds / export-voxtral-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t 2729524d41d601df5850e345d5f27578f29f1ec1a27bb87478e94a9e98ab9afa /exec failed with exit code 2
• Test Metal Backend / export-voxtral-metal-artifact / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• pull / nxp-build-test / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / test-setup-linux-gcc / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.
• Test CUDA Builds / test-models-cuda (conv1d) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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