26. Lambda Calls Without Allocation in the Closure Backend

• Each lambda call (closure.apply) copied the evaluation context and allocated a local for each parameter, and each lambda expression allocated a closure. On JSON this was 36k of the closure backend's 37k allocations per parse.
• Contexts and parameters of a call now come from LIFO arenas of the closure evaluator (arena[T] in closureMachine), freed when the call returns; closures come from an arena freed at the next evaluation (evalTerm), since a lambda cannot outlive the action or predicate that created it (lambdas are only arguments of map, foldl and foldr, and functions cannot be stored). A lambda created inside another lambda's call keeps a heap copy of that call's context (keep).
• Effect (min of 8 interleaved runs, Apple M3 Max, closure backend, code points): JSON 15.9 → 15.3 ms, 37k → 1.3k allocations, 23.6 → 21.4 MB; CSV 8.0 → 7.3 ms, 56k → 0.8k allocations, 19.0 → 15.6 MB; minilang 21k → 8k allocations. XML and Arith_OperatorsRule use no lambdas and are unchanged.