Improve PyRecEst backend documentation and invariants

[FlorianPfaff]

Summary

• Adds backend API matrix checks, documentation, tutorials, and scientific validation notes from the patch batch.
• Adds focused invariant and backend-contract coverage.

Validation

• Ran ruff check --fix on changed Python files.
• Ran git diff --cached --check.
• Scanned staged files for conflict markers.
• Tests were not run per request.

[github-actions]

✅⚠️MegaLinter analysis: Success with warnings

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	32.76s
⚠️ MARKDOWN	markdownlint	4	0	10	0	0.91s
✅ MARKDOWN	markdown-table-formatter	4	3	0	0	0.5s
✅ PYTHON	black	4	4	0	0	2.12s
✅ PYTHON	isort	4	4	0	0	0.46s
✅ REPOSITORY	checkov	yes		no	no	32.66s
✅ REPOSITORY	gitleaks	yes		no	no	12.33s
✅ REPOSITORY	git_diff	yes		no	no	0.06s
✅ REPOSITORY	secretlint	yes		no	no	11.58s
✅ REPOSITORY	syft	yes		no	no	6.5s
✅ REPOSITORY	trivy-sbom	yes		no	no	4.01s
✅ REPOSITORY	trufflehog	yes		no	no	18.1s
✅ YAML	prettier	1	0	0	0	0.48s
✅ YAML	v8r	1		0	0	1.77s
✅ YAML	yamllint	1		0	0	0.46s

Detailed Issues

⚠️ MARKDOWN / markdownlint - 10 errors

docs/scientific-validation.md:13:9 error MD060/table-column-style Table column style [Table pipe is missing space to the left for style "compact"]
docs/scientific-validation.md:13:19 error MD060/table-column-style Table column style [Table pipe is missing space to the left for style "compact"]
docs/scientific-validation.md:13:30 error MD060/table-column-style Table column style [Table pipe is missing space to the left for style "compact"]
docs/scientific-validation.md:13:1 error MD060/table-column-style Table column style [Table pipe is missing space to the right for style "compact"]
docs/scientific-validation.md:13:9 error MD060/table-column-style Table column style [Table pipe is missing space to the right for style "compact"]
docs/scientific-validation.md:13:19 error MD060/table-column-style Table column style [Table pipe is missing space to the right for style "compact"]
docs/tutorials/backend-portable-workflows.md:62:12 error MD060/table-column-style Table column style [Table pipe is missing space to the left for style "compact"]
docs/tutorials/backend-portable-workflows.md:62:32 error MD060/table-column-style Table column style [Table pipe is missing space to the left for style "compact"]
docs/tutorials/backend-portable-workflows.md:62:1 error MD060/table-column-style Table column style [Table pipe is missing space to the right for style "compact"]
docs/tutorials/backend-portable-workflows.md:62:12 error MD060/table-column-style Table column style [Table pipe is missing space to the right for style "compact"]

Notices

📣 MegaLinter 9.5.0 is out! Discover the new features and security recommendations in the release announcement. (Skip this info by defining SECURITY_SUGGESTIONS: false)

See detailed reports in MegaLinter artifacts
Set VALIDATE_ALL_CODEBASE: true in mega-linter.yml to validate all sources, not only the diff

Show us your support by starring ⭐ the repository

[github-actions]

Test Results

    10 files  +    3      10 suites  +3   2h 26m 24s ⏱️ + 1h 16m 1s
 1 987 tests +   18   1 983 ✅ +   21      4 💤  -     3  0 ❌ ±0 
20 295 runs  +6 092  16 711 ✅ +3 677  3 584 💤 +2 415  0 ❌ ±0 

Results for commit 6930c6a. ± Comparison against base commit 425985b.

♻️ This comment has been updated with latest results.