testing densification methods

[Johnnyassaf]

Purpose

• Adds a standalone Hail Batch script (test_densify_chr1.py) that reads a densification checkpoint, filters to chr1, and runs two post-densification approaches
  side-by-side for comparison:
  • Current: adjust_vcf_types before sparse_split_multi (no info adjustment after)
  • Proposed: sparse_split_multi(filter_changed_loci) first, then adjust_info and adjust_vcf_types
• Reports diagnostics for both (schema, row counts, variant drop accounting, LPL→PL downcode verification at multiallelic sites)

Proposed Changes

Checklist

• Version Bump!
• Related GitHub Issue created
• Tests covering new change
• Linting checks pass