perf: speed up kernel checking of ring and field certificates

This PR speeds up kernel checking of ring and field certificates produced by `grind` and `Sym.simp`.

Specialize monomial equality by projecting power fields directly, and inline `Bool.rec` in polynomial equality and one-pass addition checks. Add recursor-based inverse cancellation and specialized rational-polynomial equality for field certificates, with equivalence proofs, differential tests, and a scalable benchmark.

Kernel instruction counts decrease by 2.33% across 12 existing workloads, including 2.49% for `groebner_hard` and 6.57% for `sym_arith_norm_field`. The new inverse-cancellation stress benchmark uses 68.21% fewer kernel instructions. These figures use three-run medians, subtracting runs with `debug.skipKernelTC` enabled to isolate kernel checking costs.