Fix #3: list_avg handles Int32 natively (sum as i64), avoids full
  f64 cast of flat value arrays for GQ/DP averaging.

Fix #4: skip arrow::compute::filter (8 calls) when all variants
  pass site filtering — use original columns directly.

Fix #5: writer buffers entire variant line into Vec<u8> before a
  single write_all call. Eliminates ~10 tiny write syscalls per
  sample (6M → 300 writes/batch for 2000 samples). Uses itoa for
  zero-alloc integer formatting.

Fix #6: pre-computed lookup table for 10^(-PL/10) replaces 3×
  powf() per sample in dosage computation (~60ns → ~3ns each).

Fix #8: FlatNumeric enum keeps GQ/DP as native Int32, compares
  with f64 thresholds directly — no cast to Float64 then back.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…csq paradigm)

The v1 port used the retired Layer-8 oracle infrastructure:
  - port_common::run_and_compare_csq harness (golden.vcf field-by-field
    diff, with vacuity-guard + hard/soft separation)
  - tests/data/port/cache_transcript/golden.vcf (generated by retired
    gen_golden.sh script; CI-time docker oracle dependency)

Replaced under v2 by:
  - src/partitioned_cache.rs::tests (unit-ports for #5-#10)
  - src/transcript_consequence.rs::tests (Axis B B2/B3 unit-ports)
  - src/kv_cache/sift_store.rs::tests (SiftKvStore #12, #16 unit-ports)
  - src/annotate_provider.rs::tests (region-tuple math #46)
  - tests/port_cache_transcript.rs (integration #24/#39/#47/#49 + Axis B
    + 28 arch-no-analogue + 25 blocked-future-work stubs)
  - tests/port_cache_transcript_e2e.rs (#50 + #51 e2e LOAD-BEARING)

Oracle values hand-coded with `// verified via VEP 115 …` audit trail
comments per v2 paradigm Rule 2 (extracted from the v1 golden.vcf
before deletion; preserves the audit chain).

input.vcf preserved (14 chr21 variants at 25.19-26.0 Mb).

See porting-tests/plans/2026-05-28-port-cache-transcript.md.

)

Adds 6 unit-ports to src/partitioned_cache.rs::tests (mirroring the
existing RegFeat unit-ports for the transcript context_type):

- #5  transcript_serializer_label_is_parquet_for_v115_layout
- #6  transcript_context_path_uses_parquet_suffix
- #7  transcript_available_chroms_returns_chrom_list_from_layout
- #8  transcript_context_path_for_chr21_returns_per_chrom_parquet_path
- #9  transcript_context_path_takes_only_chrom_arg
- #10 transcript_context_path_with_empty_chrom_returns_none

Per detailed_plan rows #5-#10. Same v2 paradigm Rule 6 ("parquet IS
vepyr's serializer-equivalent for the same role") applied to the
transcript context_type.