8. Fast Path for Unmemoized Calls, SCAN, Nesting Limit (D2db87d)

• Unmemoized calls skip the memo bookkeeping: the examined range only grows, so it needs no save/restore, and expectations need no isolation.
• Single-character repetitions ([class]*, .+, ...) in value-free positions run as a scan loop without per-iteration backtracking state (closure: scanRepeat; bytecode: the new SCAN instruction).
• Nesting limit. Rule-call depth is capped (WithMaxDepth, default 100,000; 10,000,000 for the iterative VM). This is a robustness fix rather than a speedup: a corrupted .pegoc (for example a cleared left-recursion flag) used to recurse until the Go stack overflowed.
• Effect: recognition JSON 39 → ~32 ms, CSV 24 → 18 ms, minilang 40 → ~31 ms; full parses a few percent.