Fix cumulative operations when axis=None

[aisk]

Proposed changes

Previously, the Python bindings used workarounds by flattening arrays and operating along axis 0. Now these operations have proper C++ overloads without axis parameters that automatically flatten the arrays, following the same pattern as concatenate.

Checklist

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• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[awni]

Looks good, thanks!