Fix PyTorch Sylvester complex shortcut

[FlorianPfaff]

Summary

• Restrict the PyTorch solve_sylvester symmetric fast path to real shared symmetric factors.
• Route complex symmetric non-Hermitian inputs through the general SciPy Sylvester solver.
• Add a regression test that checks the residual for a complex symmetric non-Hermitian case.

Validation

Local numerical check: the old shortcut has a residual norm around 3.04 on the regression case, while the patched path is around 1e-15.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	45.66s
✅ JSON	prettier	7	0	0	0	1.13s
✅ JSON	v8r	7		0	0	4.64s
✅ MARKDOWN	markdownlint	66	0	0	0	1.74s
✅ MARKDOWN	markdown-table-formatter	66	0	0	0	0.78s
✅ PYTHON	black	781	0	0	0	35.81s
✅ PYTHON	isort	781	0	0	0	5.98s
✅ REPOSITORY	checkov	yes		no	no	41.78s
✅ REPOSITORY	gitleaks	yes		no	no	12.71s
✅ REPOSITORY	git_diff	yes		no	no	0.12s
✅ REPOSITORY	secretlint	yes		no	no	22.56s
✅ REPOSITORY	syft	yes		no	no	4.97s
✅ REPOSITORY	trivy-sbom	yes		no	no	5.54s
✅ REPOSITORY	trufflehog	yes		no	no	21.99s
✅ YAML	prettier	11	0	0	0	0.67s
✅ YAML	v8r	11		0	0	11.08s
✅ YAML	yamllint	11		0	0	0.4s

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