perf(rust): versor_apply f64 parity port — 29x over Python, bit-identical
Closes the last open Rust parity gate from ADR-0020.
Kernel: new versor_apply_closed_f64 in core-rs/src/versor.rs performs
the full sandwich V·F·rev(V) + closure in f64, mirroring Python's
algebra.versor.versor_apply + _close_applied_versor exactly:
- no null-vector early branch (Python doesn't have one)
- unitize_versor with dense-support seed fallback gate
- post-unitize versor_condition < 1e-6 recheck
- seed_to_rotor on failure, passthrough as last resort
PyO3 binding: versor_apply_with_closure_f64 accepts/returns float64
arrays through new extract_f64_slice / f64_array_to_numpy helpers.
algebra/backend.py::versor_apply routes through it under CORE_BACKEND=rust.
Parity gate re-enabled (was skipped pending this port). 8/8 bit-
identical across normalized hot-path + identity-versor cases.
Bench (5000 iters, runtime hot path):
python: 213.0 us/call
rust: 7.4 us/call → 28.8x speedup
All lanes green: algebra 132 (was 124+8skip), smoke 54, runtime 19,
cognition 57, teaching 17, packs 6. Cognition eval 100% across all metrics.
PROGRESS.md updated: versor_apply marked passing; Phase 5 Rust parity
track now 5/5 surfaces gated and enabled.
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