Fix hyperrectangular backend edge cases

[FlorianPfaff]

Summary

• Fix backend behavior for hyperrectangular distribution edge cases across NumPy, JAX, and PyTorch paths.
• Add regression coverage for hyperrectangular backend behavior.

Validation

• Applied patch cleanly.
• Ran scoped ruff check --fix --ignore F401,F811,E402 on changed Python files because backend __init__.py modules intentionally re-export many symbols and otherwise trigger existing export-layout lint reports.
• Ran git diff --cached --check and conflict-marker scan.

Tests were not run per request.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	24.77s
✅ PYTHON	black	6	4	0	0	2.53s
✅ PYTHON	isort	6	4	0	0	0.35s
✅ REPOSITORY	checkov	yes		no	no	24.61s
✅ REPOSITORY	gitleaks	yes		no	no	13.03s
✅ REPOSITORY	git_diff	yes		no	no	0.04s
✅ REPOSITORY	secretlint	yes		no	no	9.45s
✅ REPOSITORY	syft	yes		no	no	2.46s
✅ REPOSITORY	trivy-sbom	yes		no	no	3.26s
✅ REPOSITORY	trufflehog	yes		no	no	17.69s

Notices

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[github-actions]

Test Results

    10 files  +     9      10 suites  +9   2h 32m 48s ⏱️ + 2h 27m 9s
 1 994 tests +    25   1 990 ✅ +    35      4 💤  -    10  0 ❌ ±0 
20 365 runs  +18 324  16 775 ✅ +14 748  3 590 💤 +3 576  0 ❌ ±0 

Results for commit b762026. ± Comparison against base commit 941b015.

♻️ This comment has been updated with latest results.