Export lora weights to sep file

[lucylq]

Differential Revision: D83777195

[ghstack-poisoned]

Summary

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Test plan

[PLEASE REMOVE] How did you test this PR? Please write down any manual commands you used and note down tests that you have written if applicable.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15061

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❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• [ROCm][CI] Machines under the label linux.rocm.gpu.2 are undergoing maintenance.

❌ 4 New Failures, 12 Pending, 1 Unrelated Failure

As of commit c6c76ef with merge base a66ea20 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
• pull / test-qnn-wheel-packages-linux (3.10) / linux-job (gh)
  RuntimeError: Command docker exec -t ea9346298866fea686d6be8012a92742d73c3662547a8848d6e6a37cb18753e0 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.11) / linux-job (gh)
  RuntimeError: Command docker exec -t 65242ea50419b589859a50614c89da1c3a5b5cde49d678210b550983e7983897 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.12) / linux-job (gh)
  RuntimeError: Command docker exec -t d5b281bafe10e198384ae6357aa4a1cee0748a0df4756ce21c8752549f65d344 /exec failed with exit code 1

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

• pull / test-models-linux-basic (vit, portable, cmake, linux.2xlarge, executorch-ubuntu-22.04-clang12) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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