Fix PyTorch kron array-like backend contract

[FlorianPfaff]

Summary

• Patch raw pyrecest._backend.pytorch.kron so it accepts NumPy-style array-like inputs instead of exposing bare torch.kron.
• Keep the public PyTorch backend facade aligned when PYRECEST_BACKEND=pytorch is active.
• Add subprocess regression coverage for raw PyTorch kron under both NumPy and PyTorch public backend selections, including out= handling.

Bug fixed

torch.kron rejects Python-list inputs, while the NumPy/PyRecEst backend contract accepts array-like operands. Direct raw PyTorch calls such as pyrecest._backend.pytorch.kron([[1, 2]], [3, 4]) could therefore fail, and public PyTorch backend calls had the same issue.

Validation

• Branch is current against main at compare time (ahead_by=2, behind_by=0).
• Syntax-checked the modified backend support module and new regression test with python -m py_compile in the container.
• Full pytest was not run locally because this execution environment cannot resolve github.com for cloning/installing repository dependencies; CI should run the focused backend-portable regression.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	62.51s
✅ JSON	prettier	7	0	0	0	1.23s
✅ JSON	v8r	7		0	0	4.7s
✅ MARKDOWN	markdownlint	68	0	0	0	1.57s
✅ MARKDOWN	markdown-table-formatter	68	0	0	0	0.7s
✅ PYTHON	black	1132	4	0	0	56.68s
✅ PYTHON	isort	1132	4	0	0	2.6s
✅ REPOSITORY	checkov	yes		no	no	43.93s
✅ REPOSITORY	gitleaks	yes		no	no	8.85s
✅ REPOSITORY	git_diff	yes		no	no	0.2s
✅ REPOSITORY	secretlint	yes		no	no	46.59s
✅ REPOSITORY	syft	yes		no	no	4.17s
✅ REPOSITORY	trivy-sbom	yes		no	no	3.86s
✅ REPOSITORY	trufflehog	yes		no	no	13.93s
✅ YAML	prettier	11	0	0	0	0.67s
✅ YAML	v8r	11		0	0	10.03s
✅ YAML	yamllint	11		0	0	0.49s

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