feat: added memchr, memcmp, memmv and realloc

srcs/ft_realloc.c

@@ -0,0 +1,22 @@
+#include "libft.h"
+#include <stdlib.h>
+#include <string.h>
+
+void *ft_realloc(void *ptr, size_t old_size, size_t new_size)
+{
+    if (new_size == 0) {
+        free(ptr);
+        return (NULL);
+    }
+    if (!ptr)
+        return (malloc(new_size));
+
+    void *new_ptr = malloc(new_size);
+    if (!new_ptr)
+        return (NULL);
+
+    size_t copy_size = old_size < new_size ? old_size : new_size;
+    ft_memcpy(new_ptr, ptr, copy_size);
+    free(ptr);
+    return (new_ptr);
+}