[FEATURE] Add element_count to unexpected rows results

[BALOGUN-DAVID]

Closes #11045

Changes

• Add table.row_count as a metric dependency for UnexpectedRowsExpectation.
• Return element_count in BASIC, SUMMARY, and COMPLETE validation result payloads.
• Add regression assertions for element_count while preserving existing result_format behavior.

Tests

• .\.venv\Scripts\python.exe -m pytest tests/expectations/core/test_unexpected_rows_expectation.py -v

• .\.venv\Scripts\python.exe -m invoke lint --no-pty

• Description of PR changes above includes a link to an existing GitHub issue: Unexpected_rows_expectation doesn't give element_count in the validation results #11045

• PR title is prefixed with one of: [BUGFIX], [FEATURE], [DOCS], [MAINTENANCE], [CONTRIB], [MINORBUMP]

• Code is linted - run invoke lint (uses ruff format + ruff check)

• Appropriate tests and docs have been updated

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[BALOGUN-DAVID]

@cla-bot check

[BALOGUN-DAVID]

Hi @joshua-stauffer, here again 😀 Could you please take a look at this PR when you'red chanced lmk If everything looks good

[github-actions]

Is this PR still relevant? If so, what is blocking it? Is there anything you can do to help move it forward?

This issue has been automatically marked as stale because it has not had recent activity.

It will be closed if no further activity occurs. Thank you for your contributions 🙇