Fix sampler edge cases

[FlorianPfaff]

Summary

• fix singleton Fibonacci Gaussian/grid samples so they no longer divide by zero and return finite centered representatives
• make fixed-resolution spherical grids return the full longitude/latitude tensor product and validate positive resolutions
• make Fibonacci-Hopf integer-density grids choose an integer circle count and validate circular grid density
• fix SphericalGridDistribution.from_function(..., grid_type="driscoll_healy") so it unpacks the generated grid and uses an integer Driscoll-Healy degree
• add regression coverage for the affected Euclidean, spherical/Hopf, circular, and Driscoll-Healy spherical-grid edge cases

Validation

• Added focused regression tests in tests/test_euclidean_sampler.py, tests/test_hyperspherical_sampler.py, tests/test_hypertoroidal_sampler.py, and tests/distributions/test_spherical_grid_distribution_driscoll_healy.py
• Did not run the full test suite locally in this environment

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	29.7s
✅ PYTHON	black	8	7	0	0	3.11s
✅ PYTHON	isort	8	7	0	0	0.42s
✅ REPOSITORY	checkov	yes		no	no	33.36s
✅ REPOSITORY	gitleaks	yes		no	no	17.18s
✅ REPOSITORY	git_diff	yes		no	no	0.05s
✅ REPOSITORY	secretlint	yes		no	no	11.47s
✅ REPOSITORY	syft	yes		no	no	2.45s
✅ REPOSITORY	trivy-sbom	yes		no	no	3.43s
✅ REPOSITORY	trufflehog	yes		no	no	23.01s

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