Compile expressions once per operator, not per batch

Applies to: every Calc/filter operator

Predicates and projections are encoded at plan time and compiled to a DataFusion physical expression once per distinct input schema; earlier stateless paths re-planned per batch. A mixed insert/changelog union can require two cached schemas because only one arm carries the hidden row-kind column. Each handle is released when its owning operator closes. Removed per-batch query planning from every Calc/filter evaluation.