P9 (WIP): compiled kernels (rust/simurg-core, PyO3) with bit-identical pure-Python fallback

Rust ports of the hot paths found by profiling: fused per-locus GenCall calling
and scoring, BAF/LRR, libm maps with CPython math semantics, both nearest-neighbour
searches of the normalization fit, and the BPM LocusEntry parser. Address
coverage is memoised per IDAT layout. SIMURG_PURE_PYTHON=1 forces the pure paths.
On the Pi: genotype_sample 3.4 s -> 1.1 s, 36-sample GSA run 131 s -> 46 s, BPM
read 4x faster; 36 GSA + 6 Omni2.5 GTCs and QC tables byte-identical to the pure
path; tests/unit/test_core_kernels.py checks every kernel on edge cases.
bench/profile_genotype.py, bench/scaling.py, cloud task p9 (thread scaling).

src/simurg/pipeline/genotype.py

@@ -160,7 +160,7 @@ def _process(job: Job) -> dict[str, Any]:
     try:
         grn, red = read_idat(job.grn), read_idat(job.red)
         check_pair(grn, red)
-        _, notes = check_coverage(grn, ctx.manifest)
+        _, notes = check_coverage(grn, ctx.manifest, ctx.cache)
         row["notes"].extend(notes)
         g = genotype_sample(grn, red, ctx, params, _W["started"])
         write_gtc(g, Path(job.gtc_path))