refactor(index): use arrow stats for scalar index stats

[HaochengLIU]

Summary

• Replace zonemap DataFusion min/max accumulators with lance_arrow_stats::StatisticsAccumulator.
• Use arrow_stats to track bloom filter zone null counts.
• Keep scalar-index NaN handling local to Lance instead of importing DataFusion math UDFs.
• Add lance-arrow-stats to the lance-index dependency graph and update the Python lockfile.

Testing

• All tests pass.

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 70.11494% with 26 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance-index/src/scalar/zonemap.rs	66.21%	18 Missing and 7 partials ⚠️
rust/lance-index/src/scalar/bloomfilter.rs	92.30%	0 Missing and 1 partial ⚠️

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[claude]

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[HaochengLIU]

@claude review once

[HaochengLIU]

@westonpace @jackye1995 can any of you review this PR? ty