Disposing a checked-dynamic node released each entry's getter and setter
and the node's prototype and symbol tables through scr_dyn_release, though
almost all of them are NULL: in a zod validation loop, over half of all
dyn releases. Dispose now tests each child first.
A pooled object also walked all its slots again on reuse, to take the key
bytes it kept back from the pool's key budget. It now records that total
when it is pooled, and reuse subtracts it.
Chris Tate
cbc062a35f