Prevent manifold EMA state aliasing

[FlorianPfaff]

Bug

ManifoldExponentialMovingAverage overrides the base filter's filter_state setter and assigned states directly instead of copying them. Its first-update path also stored the caller's sample object directly.

For mutable manifold states such as NumPy arrays, mutating the original sample or replacement state after assignment therefore changed the filter estimate without another filter update. This violates the state-ownership behavior established by AbstractFilter, whose constructor and setter deep-copy assigned state.

Fix

• deep-copy values assigned through ManifoldExponentialMovingAverage.filter_state;
• route first-sample initialization through that setter;
• route retraction results through the same setter so all state writes follow one ownership contract.

Regression coverage

Add focused tests verifying that:

• the first sample can be mutated after update(...) without changing the stored estimate;
• an array assigned through filter_state can be mutated afterward without changing the stored estimate.

Validation

• reproduced the old aliasing behavior: changing the input array changed the stored state from [2, 3] to [-1, -1];
• verified the corrected ownership behavior preserves [2, 3];
• syntax-compiled both changed Python modules;
• checked both changed files for the repository's 88-column limit;
• branch comparison: 2 commits ahead and 0 behind main;
• final diff is limited to 4 additions / 3 deletions in the implementation and one focused regression module.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	26.36s
✅ JSON	prettier	7	0	0	0	0.91s
✅ JSON	v8r	7		0	0	3.12s
✅ MARKDOWN	markdownlint	68	0	0	0	1.83s
✅ MARKDOWN	markdown-table-formatter	68	0	0	0	0.65s
✅ PYTHON	black	1866	87	0	0	91.14s
✅ PYTHON	isort	1866	140	0	0	2.75s
✅ REPOSITORY	betterleaks	yes		no	no	2.55s
✅ REPOSITORY	checkov	yes		no	no	48.4s
✅ REPOSITORY	gitleaks	yes		no	no	17.22s
✅ REPOSITORY	git_diff	yes		no	no	0.33s
✅ REPOSITORY	secretlint	yes		no	no	85.6s
✅ REPOSITORY	syft	yes		no	no	5.75s
✅ REPOSITORY	trivy-sbom	yes		no	no	6.02s
✅ REPOSITORY	trufflehog	yes		no	no	30.79s
✅ YAML	prettier	11	0	0	0	0.73s
✅ YAML	v8r	11		0	0	10.94s
✅ YAML	yamllint	11		0	0	0.55s

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