Infrastructure for ViaKoopman Proof

This file re-exports infrastructure from split modules:

• InfraCore: Two-sided extension, instance-locking shims, CE pullback
• InfraLagConstancy: Lag-constancy from exchangeability
• InfraGeneralized: Generalized lag-constancy, CE helpers

Import this file to get all infrastructure in one import.

Split into: InfraCore.lean, InfraLagConstancy.lean, InfraGeneralized.lean