Add opt-in ring far-field evaluation for WASM 0.8.0

[andrekuehne]

Dense upper-hemisphere grids spend most retained-solve time evaluating far fields. This adds an opt-in ring band-limited evaluator and prepares @necpp-engine/wasm 0.8.0, while keeping existing exact defaults and goldens unchanged.

Set farFieldEvaluator: "ring" when creating a model or array solver, or select evaluator per request. The shared C++ kernel supports free space and PEC ground, falls back to direct evaluation when needed, and works with ordinary fields, worker pools, both embedded normalizations, and packed characterization. Result metadata records evaluator provenance and the analytical truncation bound; packed formats and ABI version 1 remain compatible.

The report in docs/ring-far-field-evaluation.md includes profiling, the tail-bound derivation, native/WASM benchmarks, accuracy, limitations, and reproduction commands. Large-array stateful WASM field evaluations improved 6.76–8.91×. All 154 benchmark comparisons passed the 1e-7 target (largest observed relative error 5.389e-10); all 84 scalar power-closure comparisons agree to nine decimal places.

Validation:

• Eight native CTest groups, 160 package tests, and TypeScript checking passed.
• Package manifest, README examples, clean Node/CDN/Vite consumers, and browser worker/packed-handoff checks passed.
• Rechecked the 0.8.0 package identity, manifest, and consumers; built a local candidate with the release packer.

The version bump updates the lockfile, runtime version export, fixture version metadata, assertions, and changelog. No npm publication or visualizer dependency change is included. The visualizer can use the CI-tested 0.8.0 tarball from this PR/merge workflow using its existing vendoring process.