WIP: P2 rendering

 - Replaced the std::map<MeshKey, StaticDrawCommand> hot draw lists with unordered_map buckets plus sorted traversal vectors.
 - Added stable draw ordering by pipeline, shader, material, then mesh.
 - Added conservative shadow map caching using caster hashes, spot-light hashes, and directional light/camera cascade state.
 - Added cascade update thresholds so tiny camera/light changes do not constantly rebuild cascades.
 - Shadow passes now skip rendering when cached shadow maps are still valid.

Author: sheazywi