fuzz: add OSC parser fuzzer

test/fuzz-libghostty/src/mem.zig

@@ -0,0 +1,26 @@
+const std = @import("std");
+
+/// 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.
+pub fn FuzzAllocator(comptime mem_size: usize) type {
+    return struct {
+        buf: [mem_size]u8 = undefined,
+        state: std.heap.FixedBufferAllocator = undefined,
+
+        const Self = @This();
+
+        pub fn init(self: *Self) void {
+            self.state = .init(&self.buf);
+        }
+
+        pub fn allocator(self: *Self) std.mem.Allocator {
+            return self.state.allocator();
+        }
+
+        pub fn reset(self: *Self) void {
+            self.state.reset();
+        }
+    };
+}