feat: add ft_memcpy function

ft_memcpy.c

@@ -0,0 +1,18 @@
+#include "libft.h"
+
+void	*ft_memcpy(void *dst, const void *src, size_t n)
+{
+	size_t	i;
+	char	*srctmp;
+	char	*dsttmp;
+
+	i = 0;
+	srctmp = (char *)src;
+	dsttmp = (char *)dst;
+	while (i < n)
+	{
+		dsttmp[i] = srctmp[i];
+		i++;
+	}
+	return (dst);
+}