Cortex-M backend: Minimize scope of cmsis_nn dependency.

[Erik-Lundell]

For Ethos-U flows, you might want to run only the ReplaceQuantNodesPass pass which doesn't require the cmsis_nn dependency. Since the install is currently not trivial, we shouldn't force people to do it when not needed.
Right now, all passes are imported when importing that pass, triggering importing cmsis_nn.

• Only require cmsis_nn when cmsis_nn functions are used.
• Do this by wrapping cmsis_nn, taking the chance to add typing.

Tested by running
from executorch.backends.cortex_m.passes import ReplaceQuantNodesPass

Before the patch this triggers an error if cmsis_nn is not installed. After the patch, it doesn't.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani @psiddh @AdrianLundell

[pytorch-bot]

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❌ 2 New Failures, 2 Unrelated Failures

As of commit bfea4e5 with merge base 3707efa ():

NEW FAILURES - The following jobs have failed:

• pull / test-lora-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 2734612a3278eab4520e5e46f716f71219b075abc81c3aa2ab034cb4ad037e9d /exec failed with exit code 1
• pull / test-lora-multimethod-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 030ad28157ba4ea29a6678c98e2063e2e2b2527e70bc51dfcbad2a93b69a45a3 /exec failed with exit code 1

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

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

• pull / test-llama-runner-qnn-linux (fp32, qnn_16a16w, qnn) / linux-job (gh) (trunk failure)
• trunk / test-llama-runner-qnn-linux (fp32, qnn_16a16w, qnn) / linux-job (gh) (trunk failure)

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