perf: use range query kernel for wide dual ranges

[samukweku]

Summary

• use the janitor-rs direct range min/max kernel for wide unsorted dual-range selections
• retain existing sorted-right, width-one, unsupported-dtype, and narrow-workload paths
• fall back cleanly when the installed janitor-rs extension does not expose the new functions
• add focused dispatch tests for first/last selection and fallback behavior

The supporting janitor-rs PR is pyjanitor-devs/janitor-rs#111.

Performance

End-to-end prototype timings on wide unsorted dual-range joins:

• 10,000 rows: 9.4 ms -> 3.3 ms
• 100,000 rows: 111 ms -> 36 ms

Validation

• conditional_join suite: 241 passed, 1 skipped
• dispatch + conditional_join suite: 245 passed, 1 skipped
• randomized parity: 100 seeds x both keep modes
• pre-commit hooks for changed files passed; repository-wide lint still reports pre-existing unrelated violations

Fixes #1652

[github-actions]

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