Arm backend: Do not delegate casting to FP dtypes with BI profile

[YufengShi-dudu]

• Casting to floating-point dtypes should be rejected for delegation. Class ToCopySupported should guarantee this. However, the shallow copy used in func _merge_supported_types will modify the dict SUPPORTED_INT_TYPES unintentionally, merging the dict SUPPORTED_FLOAT_TYPES into SUPPORTED_INT_TYPES. Therefore, casting to floating-point dtypes can also pass the check under BI profile.
• Fix it by using deepcopy.
• Add unittest in test_to_copy.py to check the castings to FP dtypes are not delegated.

Change-Id: Ia5fce0c0284aa35fcd5a482fe11985573a00db8b

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218

[pytorch-bot]

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❌ 1 New Failure, 1 Pending, 1 Unrelated Failure

As of commit b78b885 with merge base d069d65 ():

NEW FAILURE - The following job has failed:

• Apple / build-benchmark-app / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1

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

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

• pull / test-llava-runner-linux / linux-job (gh) (trunk failure)
  test_llava_export

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[YufengShi-dudu]

Unstable/Flaky tests:

-pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (pull_request)
test_native_layer_norm_tosa_BI[randn_last_three_dims_no_bias]

-trunk / test-arm-backend (test_pytest_ops_ethosu_fvp) / linux-job (push)
backends/arm/test/ops/test_mul.py::test_mul_tensor_tosa_BI[op_mul_rank2_rand]

[zingo]

I rebased it to trigger a test re-run to see if we can get the Arm tests green

[zingo]

That worked, Arm tests are OK and other are as you mention unrelated