Add explicit resident GPU MLS polynomial smoothing

[rsasaki0109]

MLS surface fitting still ran on the host after reusable GPU neighborhoods became available. Add explicit filter-mls-gpu position/filter APIs and resident GpuMlsInput/input-bound neighborhoods/owned results. Radius search, weighted frames and order-0/1/2 fits run on GPU; three fitting/validity passes share one submission, with private scratch leases and per-runtime pipelines. CPU tree construction and schema/attribute reconstruction remain, and all payload transfers are reported. Overflow, malformed rows and numerical errors invalidate all device output and reject at explicit download.

Results expose original-order unchanged/plane/polynomial modes and counts. GPU normalized f32 Cholesky uses a relative rank test; existing CPU f64 Gaussian elimination is unchanged. Nearly singular fits can differ substantially: the adverse 65-point quadratic fixture differs by 0.97287786 from the requested CPU result (52 GPU plane fallbacks), retained separately from mode-reference errors. This opt-in API does not promise CPU coordinate/fallback parity.

Two isolated release surveys retain all 24 conditions and 20 paired samples per stage. At 65,537 points, complete GPU filter calls including preparation, transfers, wait and reconstruction measure 1.61-3.45x against the current four-worker CPU filter; 257-point GPU calls are slower. Resident timings exclude preparation/upload/search/readback. Outcome counts, both coordinate error measures, variability and bootstrap intervals are included in the evidence note.

Validation passed: 207 GPU tests; 40 filtering library tests; four explicitly run adapter integrations covering 135 conditions / 205,470 coordinates, ownership/concurrency, invalid rows and exact schema/metadata/attribute bits; one facade GPU test. Independent quadratic-spike and noisy-plane tests confirm polynomial fitting and about 81% RMS reduction. All-feature and CPU-only Clippy, minimal GPU, WASM feature compilation and Rustfmt passed. Add two feature-isolation CI jobs; hosted compilation does not replace native adapter evidence.