This adds a `test/fuzz-libghostty` which is a standalone `zig build`
target for building an AFL++ instrumented executable for fuzzing the
libghostty-vt parser. I also added a `pkg/afl++` (based on zig-afl-kit)
so instrumenting objects and using AFL++ is a bit easier.
Fuzzing `libghostty-vt`'s parser is as easy as `zig build run`, but see
the README for a lot more details. I ran the fuzzer for ~14 hours total
and only found one crash #11088. I'm pretty confident at this point our
Parser layer isn't obviously crash-able, but need to instrument more
places to fuzz.
We don't use Zig's built-in fuzzing yet because as of 0.15 (our current
stable), it isn't ready and AFL++ is an industry proven tool to do this.
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