Fix PyTorch concatenate axis=None contract

[FlorianPfaff]

Summary

• patch the PyTorch backend compatibility hook so concatenate(..., axis=None) flattens each input before concatenating, matching NumPy/JAX behavior
• keep the raw pyrecest._backend.pytorch.concatenate contract patched even when another public backend is selected
• add subprocess regression tests for both public PyTorch and raw PyTorch under a NumPy public backend

Bug

On current main, pyrecest._backend.pytorch.concatenate(..., axis=None) forwards dim=None to torch.cat, which raises instead of applying NumPy's documented flattening behavior.

Tests

• Not run locally in this environment; added targeted backend-portable regression tests for CI.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	62.25s
✅ JSON	prettier	7	0	0	0	0.99s
✅ JSON	v8r	7		0	0	4.44s
✅ MARKDOWN	markdownlint	68	0	0	0	1.57s
✅ MARKDOWN	markdown-table-formatter	68	0	0	0	0.85s
✅ PYTHON	black	1133	5	0	0	53.71s
✅ PYTHON	isort	1133	5	0	0	2.94s
✅ REPOSITORY	checkov	yes		no	no	42.95s
✅ REPOSITORY	gitleaks	yes		no	no	11.46s
✅ REPOSITORY	git_diff	yes		no	no	0.25s
✅ REPOSITORY	secretlint	yes		no	no	41.51s
✅ REPOSITORY	syft	yes		no	no	3.69s
✅ REPOSITORY	trivy-sbom	yes		no	no	4.92s
✅ REPOSITORY	trufflehog	yes		no	no	16.0s
✅ YAML	prettier	11	0	0	0	0.71s
✅ YAML	v8r	11		0	0	10.39s
✅ YAML	yamllint	11		0	0	0.49s

Notices

📣 MegaLinter 9.5.0 is out! Discover the new features and security recommendations in the release announcement. (Skip this info by defining SECURITY_SUGGESTIONS: false)

See detailed reports in MegaLinter artifacts

Your project could benefit from a custom flavor, which would allow you to run only the linters you need, and thus improve runtime performances. (Skip this info by defining FLAVOR_SUGGESTIONS: false)

• Documentation: Custom Flavors
• Command: npx mega-linter-runner@9.5.0 --custom-flavor-setup --custom-flavor-linters PYTHON_BLACK,PYTHON_ISORT,COPYPASTE_JSCPD,JSON_V8R,JSON_PRETTIER,MARKDOWN_MARKDOWNLINT,MARKDOWN_MARKDOWN_TABLE_FORMATTER,REPOSITORY_CHECKOV,REPOSITORY_GIT_DIFF,REPOSITORY_GITLEAKS,REPOSITORY_SECRETLINT,REPOSITORY_SYFT,REPOSITORY_TRIVY_SBOM,REPOSITORY_TRUFFLEHOG,YAML_PRETTIER,YAML_YAMLLINT,YAML_V8R

Show us your support by starring ⭐ the repository