v0.39.0

Feat

• flat-variants: accept str/bytes/NucleotideAlphabet for VarWindowOpt.token_alphabet
• svar2: support spliced variant records
• svar2: scatter-write FFI entry for read-bound haplotypes
• reverse: rc_bounded_rows_inplace for scattered rows

Fix

• svar2: deterministic tie-break for scatter-write bounds sort
• svar2: validate out_bounds and to_rc in scatter-write FFI entry
• reference: reject in_memory=False with reordered/subset contigs (#285)

Refactor

• svar2: per-row destination bounds in the reconstruct core

Perf

• svar2: vectorize build_splice_plan permutation
• svar2: scatter-write spliced haplotypes, no Python re-order