Preserve wrapped-normal subclasses in operations

[FlorianPfaff]

Summary

Fix a subclass-erasure bug in WrappedNormalDistribution analogous to the subclass-preservation regressions already fixed for von Mises, vMF, Gaussian, SO(3), and grid distributions.

from_moment, shift, convolve, and the VM-based multiplication path constructed WrappedNormalDistribution directly (or converted back through the base class), so calling these APIs through a subclass silently returned the base class and discarded subclass behavior/state.

Changes

• make from_moment a classmethod and construct via cls
• make shift preserve the runtime type
• make convolve preserve the left-hand runtime type
• make multiply, multiply_vm_approximation, and multiply_vm preserve the left-hand runtime type
• add focused subclass-preservation regressions

Regression covered

Before this patch, each of the following returned WrappedNormalDistribution instead of MyWrappedNormal:

class MyWrappedNormal(WrappedNormalDistribution):
    pass

left = MyWrappedNormal(0.3, 0.8)
right = WrappedNormalDistribution(0.4, 0.6)

left.shift(0.2)
left.convolve(right)
left.multiply(right)
MyWrappedNormal.from_moment(left.trigonometric_moment(1))

The numerical algorithms are unchanged; only result construction now preserves the requested/runtime subclass.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Max errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no		no	6.94s
✅ JSON	prettier	7	0	0		0	0.76s
✅ JSON	v8r	7		0		0	5.47s
✅ MARKDOWN	markdownlint	68	0	0		0	2.14s
✅ MARKDOWN	markdown-table-formatter	68	0	0		0	0.41s
✅ PYTHON	black	2013	27	0		0	67.25s
✅ PYTHON	isort	2013	43	0		0	2.92s
✅ REPOSITORY	betterleaks	yes		no		no	1.31s
✅ REPOSITORY	checkov	yes		no		no	36.04s
✅ REPOSITORY	git_diff	yes		no		no	0.14s
✅ REPOSITORY	secretlint	yes		no		no	106.42s
✅ REPOSITORY	syft	yes		no		no	2.54s
✅ REPOSITORY	trivy-sbom	yes		no		no	2.97s
✅ YAML	prettier	11	0	0		0	0.69s
✅ YAML	v8r	11		0		0	17.54s
✅ YAML	yamllint	11		0		0	1.02s

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