Use Memcpy in copy_utils

[ethansfng]

Summary:
standard elementwise copy in copy_utils is inefficient, use memcpy instead

Rollback Plan:

Differential Revision: D76061894

[pytorch-bot]

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❌ 2 New Failures, 1 Cancelled Job, 2 Unrelated Failures

As of commit 2d907bc with merge base aed9c7e ():

NEW FAILURES - The following jobs have failed:

• Lint / lintrunner / linux-job (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 / unittest-editable / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• Lint / android-java-format / linux-job (gh)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

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

• pull / test-binary-size-linux-gcc / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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

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

• pull / test-models-linux (emformer_transcribe, portable, linux.2xlarge) / linux-job (gh) (trunk failure)

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This pull request was exported from Phabricator. Differential Revision: D76061894

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This pull request was exported from Phabricator. Differential Revision: D76061894