v0.42.0

Feat

• write: preflight the svar2 range cache and accept max_mem
• concat: verify variants.arrow fingerprint at open
• concat: tracks, annot tracks, and svar/svar2 backends
• concat: gvl.concat entry point for PGEN/VCF-backed datasets
• concat: buffered streaming IO primitives
• concat: preconditions and variants.arrow fingerprint
• concat: provenance map and run coalescing for dataset merge

Fix

• write: bound svar2 genotype-writing memory with max_mem
• concat: scope duplicate-coordinate guard to axis="regions"
• concat: close tie-order/schema gaps and drop full-array copies
• concat: verify annot-track data agrees before copying on sample axis
• concat: resolve has_dosages/fingerprint from the real store, enforce one variant source