Qualcomm AI Engine Direct - Fix static cache

[chenweng-quic]

Summary

• Fix static cache used by t5 and whisper
• Fix online prepare on Mutable buffer
• Fix minor issues

Test plan

python ${EXECUTORCH_ROOT}/backends/qualcomm/tests/test_qnn_delegate.py -k test_t5 --model SM8650 --build_folder build-android --host <host> --device <device_id>--executorch_root ${EXECUTORCH_ROOT} --artifact_dir ./t5_artifact --qa_dataset SQuAD-v1.1.csv
python ${EXECUTORCH_ROOT}/backends/qualcomm/tests/test_qnn_delegate.py -k test_whisper --model SM8650 --build_folder build-android --host <host> --device <device_id>--executorch_root ${EXECUTORCH_ROOT} --artifact_dir ./whisper_artifact_dir

cc @cccclai @cbilgin

[pytorch-bot]

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❌ 2 New Failures, 1 Unrelated Failure

As of commit 9f33327 with merge base c730feb ():

NEW FAILURES - The following jobs have failed:

• Build Presets / apple (ios) / build (gh)
• Build Presets / apple (pybind) / build (gh)
  Process completed with exit code 1.

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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[mergennachin]

See inline comments

[cccclai]

There is lint error, can you fix it?