MemLeak persistent mode

The `MemLeak` module is really nifty, but it would be nice if there were a way to (optionally) automatically persist leaked memory to a file, such that subsequent script executions can load the cached / persisted leaked memory from file, instead of leaking again over-the-wire.

This would be useful for deterministic, memory-scanning-heavy operations like Pwnable.kr's `Exynos` challenge.

Start by locating the MemLeak module and reviewing how its current leak behavior is exercised. Define the persistence interface and file behavior before implementation; done means an optional persisted leak file can be reused by subsequent script executions so deterministic scans do not leak the same memory over the wire again.

Written by the indexing model from the issue text.