This is an end-to-end fuzzer that executes arbitrary PHP code.
We replace the executor with a finite-step executor to avoid
getting stuck in loops or recursion.
We're getting some very large inputs (~500KB) on OSS-Fuzz, which
slot down performance a lot. Let's try limiting this, starting
with a still fairly large value of 64KB.
Also remove the max_execution_time limit, so that slow test cases
cause a genuine libfuzzer timeout and we may investigate them.
