Runtime Approximation Core

Backend-independent predicates and tolerance budgets for runtime-to-spec approximation.

This layer provides:

• ApproxTol, the absolute/relative/slack tolerance object used for “close enough” claims;
• scalar approximation predicates over ℝ;
• tensor/context approximation predicates that compare runtime tensors after mapping them into the real-valued spec world.

It deliberately contains no rounding model, no FP32 specialization, and no graph semantics. Those are layered on top by NN.Proofs.RuntimeApprox.Rounding, NN.Proofs.RuntimeApprox.Graph, NN.Proofs.RuntimeApprox.NF, and NN.Proofs.RuntimeApprox.FP32.