Version 0.15.0 alpha 19

• fix(call): get_repeat_count logic and performance
• fix(call): impose max iters on ref cn getter + fix ref cn logic
• fix(call): missing lock call for phase set counter
• fix(call): locking logic + SNV flip logic; make SNV calls tuples
• fix: use Union type hint for py3.9 compat
• chore(call): reduce a lock acquire timeout
• perf(call): fetch from ref FASTA 1-2 times per locus instead of 3-4
• perf(call): cache ref total seq for use in realign; log slow ref cn counting

Full Changelog: v0.15.0-alpha.18...v0.15.0-alpha.19