Make DP birth updates atomic on validation failures

[FlorianPfaff]

Summary

Fixes a state-consistency bug in DirichletProcessBirthMultiBernoulliTracker: birth-atom pruning/cap validation and Bernoulli construction could fail only after a new or reused DP birth atom had already been committed, leaving partial tracker state behind.

Changes

• validate DP birth pruning/cap controls before mutating birth atoms
• update reused atoms on a copy and commit only after component construction succeeds
• delay diagnostics/state commits until all failure-prone work completes
• add regressions for invalid atom caps, invalid pruning thresholds, and late Bernoulli-construction failures

Expected behavior

Failed birth updates now leave both birth_atoms and last_birth_diagnostics unchanged. Successful and clutter-only birth decisions retain their existing behavior.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Max errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no		no	5.05s
✅ JSON	prettier	7	0	0		0	0.47s
✅ JSON	v8r	7		0		0	3.9s
✅ MARKDOWN	markdownlint	68	0	0		0	1.31s
✅ MARKDOWN	markdown-table-formatter	68	0	0		0	0.29s
✅ PYTHON	black	2026	6	0		0	46.36s
✅ PYTHON	isort	2026	9	0		0	2.0s
✅ REPOSITORY	betterleaks	yes		no		no	1.03s
✅ REPOSITORY	checkov	yes		no		no	29.46s
✅ REPOSITORY	git_diff	yes		no		no	0.09s
✅ REPOSITORY	secretlint	yes		no		no	74.92s
✅ REPOSITORY	syft	yes		no		no	1.95s
✅ REPOSITORY	trivy-sbom	yes		no		no	1.74s
✅ YAML	prettier	11	0	0		0	0.39s
✅ YAML	v8r	11		0		0	8.99s
✅ YAML	yamllint	11		0		0	0.52s

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