Include stdlib.h to fix this error when including this header:

/opt/local/include/libfmt11/fmt/format.h:747:28: error: use of undeclared identifier 'malloc'
  747 |     T* p = static_cast<T*>(malloc(n * sizeof(T)));
      |                            ^~~~~~

https://github.com/fmtlib/fmt/commit/b77a7516251d21aef1c6130dad116edff1a13173
--- include/fmt/format.h.orig	2025-05-03 11:36:27.000000000 -0500
+++ include/fmt/format.h	2026-03-10 11:20:35.000000000 -0500
@@ -41,6 +41,8 @@
 #include "base.h"
 
 #ifndef FMT_MODULE
+#  include <stdlib.h>  // malloc, free
+
 #  include <cmath>    // std::signbit
 #  include <cstddef>  // std::byte
 #  include <cstdint>  // uint32_t