fix: Improve Validation Output, Declarative Config Consistency, and Docs

[flitzpiepe93]

Improve Validation Output, Declarative Config Consistency, and Docs

✅ Summary

This PR introduces several meaningful improvements across the validation logic and documentation:

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🧪 Validation Improvements

• _dq_errors output refined
  The fail record output now contains only actual validation failures per row — removing padded null values for passed checks.

• ValidationSummary now has a readable __str__()
  A clean, human-friendly output for quick diagnostics or CLI logs:

  ✅ Validation Summary (2025-05-11 14:30:01)
  Total records:   3,475,226
  Passed records:  3,252,514
  Failed records:    222,712
  Warnings:                 0
  Pass rate:           94.00%
  

• Declarative config parsing now enforces kebab-case
  Keys like smaller-column and greater-column are now properly supported — consistent with all other check parameters.

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📚 Documentation Enhancements

• ✅ Fixed missing BatchDQEngine import in example
• ✅ Renamed regex-match-check file for improved clarity
• ✅ Added illustration to Integration Patterns section of Sphinx docs

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🔗 Related Commits

• fix(check-runner): _dq_errors contains only validation failures
• fix(check-definition): enforce kebab-case for check definition
• fix(validation-summary): add string representation of validation summary
• docs(sphinx): add correct import to example
• docs(sphinx): renamed filename of regex-match-check
• docs(sphinx): add image to section Integration Patterns

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Let me know if this should be split across changelog categories or released under a patch version.

[codecov]

Codecov Report

Attention: Patch coverage is 97.22222% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
sparkdq/engine/batch/check_runner.py	90.90%	0 Missing and 1 partial ⚠️

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