Arm backend: Adjust AvgPool2d padding when window is not divisible by stride

[tom-arm]

• AvgPool2dVisitor will adjust the padding so the pooling window is divisible by the stride
• Improve tests in test_max_pool.py

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218

[pytorch-bot]

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❌ 1 New Failure, 1 Unrelated Failure

As of commit 796dbad with merge base b73f9d5 ():

NEW FAILURE - The following job has failed:

• pull / unittest-editable / linux / linux-job (gh)
  extension/llm/modules/test/test_position_embeddings.py::TiledTokenPositionalEmbeddingTest::test_tiled_token_positional_embedding_et

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

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

• trunk / test-llama-runner-mac (fp32, coreml) / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[zingo]

Rebased after Arm test fixes

[zingo]

test fails unrelated