v0.43.0

BREAKING CHANGE

• datasets written by 0.43.0+ cannot be opened by earlier
  GenVarLoader, which fails with KeyError: 'vk_snp_range'. Reading older datasets
  is unaffected. Re-run gvl.write to shrink an existing dataset; there is no
  migration tool.

Feat

• concat: merge svar2 range caches by region batch
• svar2: project the range cache from realized fill
• svar2: write the range cache sparsely
• svar2: add the sparse region-CSR range layout
• threads: let a dataset state its own parallelism policy

Fix

• svar2: name the offending cell id, not the maximum beside it
• harden svar2 sparse range cache against silent-error regressions
• docs: correct svar2 accumulator GB figures and add genome-wide size
• svar2: guard sparse writer preconditions that corrupted silently
• svar2: cross-check dense vk shapes, align lookup input handling
• svar2: validate CSR invariants, bound entries_for_regions, bind Protocol
• ci: cache the 1kg Zenodo source and retry the download
• svar2: account for indels in haplotype_lengths

Refactor

• concat: clear final-review findings on analytic run planning
• concat: dedupe region-only plan, tighten docstring/comments from review
• svar2: read ranges through a layout protocol
• haps: split the Haps role from its SVAR1 implementation
• haps: dispatch track realignment through the reconstructor
• haps: measure variant payload through the reconstructor
• haps: query the reconstructor, not SVAR1 storage

Perf

• svar2: consume genoray's sparse range stream in the writer
• concat: yield source-dataset uniques from slot_batches
• concat: plan every merge through RunPlan, dropping the provenance map
• concat: build merged offsets from slot batches, cumsum in place
• concat: add vectorized slot batches and analytic slot count to RunPlan
• concat: derive merge runs from order without materializing slots
• svar2: add the sparse range-lookup benchmark gate
• svar2: stop allocating a dense n_variants at open
• svar2: cut the ascending-cell-id guard from ~25n to ~n bytes
• write: replace O(S^2) svar2 sample_cols with a hash lookup
• svar2: stop re-doing work on the read-bound spliced path