fuzz: add OSC parser fuzzer

test/fuzz-libghostty/src/fuzz_stream.zig

@@ -1,12 +1,13 @@
 const std = @import("std");
 const ghostty_vt = @import("ghostty-vt");
+const mem = @import("mem.zig");
 const Terminal = ghostty_vt.Terminal;
 const ReadonlyStream = ghostty_vt.ReadonlyStream;
 
 /// Use a single global allocator for simplicity and to avoid heap
 /// allocation overhead in the fuzzer. The allocator is backed by a fixed
 /// buffer, and every fuzz input resets the bump pointer to the start.
-var fuzz_alloc: FuzzAllocator = .{};
+var fuzz_alloc: mem.FuzzAllocator(64 * 1024 * 1024) = .{};
 
 pub export fn zig_fuzz_init() callconv(.c) void {
     fuzz_alloc.init();
@@ -50,29 +51,3 @@ pub export fn zig_fuzz_test(
             std.debug.panic("next: {}", .{err});
     }
 }
-
-/// Fixed-capacity allocator that avoids heap allocation and gives the
-/// fuzzer deterministic, bounded memory behaviour. Backed by a single
-/// fixed buffer; every `reset()` returns the bump pointer to the start
-/// so the same memory is reused across iterations.
-const FuzzAllocator = struct {
-    buf: [mem_size]u8 = undefined,
-    state: std.heap.FixedBufferAllocator = undefined,
-
-    /// 64 MiB gives the fuzzer enough headroom to exercise terminal
-    /// resizes, large scrollback, and other allocation-heavy paths
-    /// without running into out-of-memory on every other input.
-    const mem_size = 64 * 1024 * 1024;
-
-    fn init(self: *FuzzAllocator) void {
-        self.state = .init(&self.buf);
-    }
-
-    fn allocator(self: *FuzzAllocator) std.mem.Allocator {
-        return self.state.allocator();
-    }
-
-    fn reset(self: *FuzzAllocator) void {
-        self.state.reset();
-    }
-};