Evaluator memo

The compile memo is keyed on the trimmed text, holds no values, runs after the unsafeEval and grammar checks, is bounded and per kernel. resolveBranchScope without secret scopes equals the original walk and flips when a scope is declared.

On dist, with the values 4.2.0 gives for the same scripts: formulas follow their inputs on memo hits, the memo is cleared at every secret epoch, the fast path flips at the first scope, scoped answers hold after hydrate and replay.