fix: add cstddef include for ptrdiff_t on macOS

Fixes compilation error on macOS with conda environments where ptrdiff_t
is not resolved. This is required for libc++ on certain macOS SDK versions.

Error: reference to unresolved using declaration for ::ptrdiff_t

Author: sameeul

src/filepattern/cpp/pattern.hpp

@@ -10,6 +10,7 @@
  */
 
 #pragma once
+#include <cstddef>
 #include <string>
 #include <iostream>
 #include <vector>