vlib: add mut for the first parameter of builtin.copy, arrays.copy and crypto (#13702)

vlib/arrays/arrays.v

@@ -544,7 +544,7 @@ fn swap_nonoverlapping<T>(x_ &T, y_ &T, count int) {
 // copy copies the `src` array elements to the `dst` array.
 // The number of the elements copied is the minimum of the length of both arrays.
 // Returns the number of elements copied.
-pub fn copy<T>(dst []T, src []T) int {
+pub fn copy<T>(mut dst []T, src []T) int {
 	min := if dst.len < src.len { dst.len } else { src.len }
 	if min > 0 {
 		blen := min * int(sizeof(T))

vlib/arrays/arrays_test.v

@@ -268,16 +268,16 @@ fn test_rotate_left_string() {
 fn test_copy() {
 	mut a := [1, 2, 3]
 	mut b := [4, 5, 6]
-	assert copy(b, a) == 3
+	assert copy(mut b, a) == 3
 	assert b == [1, 2, 3]
 	// check independent copies
 	b[0] = 99
 	assert a[0] == 1
 	// check longer src
 	b << 7
-	assert copy(a, b) == 3
+	assert copy(mut a, b) == 3
 	assert a == [99, 2, 3]
 	// check longer dst
-	assert copy(b, [8, 9]) == 2
+	assert copy(mut b, [8, 9]) == 2
 	assert b == [8, 9, 3, 7]
 }