Cortex_m backend: Fix add implementation

[AdrianLundell]

• Call CMSIS-NN kernel with correct argument order and signs
• Change python implementation to reflect CMSIS-NN behaviour
• Fix scale calculations
• Remove broken broadcasting support
• Add pass to lower scalar version ops
• Remove unused definitions/ implementations in operators.py, operators.yaml and op_quantized_add.cpp

Note: arm_elementwise_add_s8 does not natively support broadcasting, so simply resizing the output tensor will not work. Enabling this in an efficient way is not straight forward, so avoid fusing these ops for now to avoid break graphs.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 7 New Failures, 4 Unrelated Failures

As of commit 8b68170 with merge base 73f7286 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 7fb1ba35213eb5ced469bf15d867de4105158085f6ac719275ffdecaee775418 /exec failed with exit code 1
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t 94a0befb5f02d0abd72221462061a10018a6b6ec2e281f56fa6c499fc18346a1 /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t e018987cc0d4b64cb924ec2957a5108af001be75267c700c9acaaea4d87fdf60 /exec failed with exit code 1
• Test CUDA Builds / export-voxtral-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t 1b317972e0706f7fc6c58f70d04dec47f7da1e8559a4a80bd403213e43580ded /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t 0f5d45ef14092aebaf9d351016446131d31d0fd4688979d3c2da2caf0cc77d10 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-weight-only / linux-job (gh)
  RuntimeError: Command docker exec -t 214274a0a8eae5c33c386da2da6fae01955b18682638931796299f6f10dc1083 /exec failed with exit code 2
• Test Metal Backend / export-voxtral-metal-artifact / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 2

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

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

• Build documentation / build (buck2) / Build doc (gh) (trunk failure)
• pull / android / run-emulator (gh) (trunk failure)
  The process '/usr/bin/sh' failed with exit code 255
• pull / unittest / linux / linux-job (gh) (trunk failure)
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)

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