atoi.v: add common_parse_uint2 with error code return values (#6550)

vlib/strconv/atoi_test.v

@@ -26,3 +26,37 @@ fn test_parse_int() {
 	assert strconv.parse_int('123', 10, 65) == 0
 	assert strconv.parse_int('123', 10, -1) == 0
 }
+
+fn test_common_parse_uint2() {
+	mut result, mut error := strconv.common_parse_uint2('1', 10, 8)
+	assert result == 1
+	assert error == 0
+
+	result, error = strconv.common_parse_uint2('123', 10, 8)
+	assert result == 123
+	assert error == 0
+
+	result, error = strconv.common_parse_uint2('123', 10, 65)
+	assert result == 0
+	assert error == -2
+
+	result, error = strconv.common_parse_uint2('123', 10, -1)
+	assert result == 0
+	assert error == -2
+
+	result, error = strconv.common_parse_uint2('', 10, 8)
+	assert result == 0
+	assert error == 1
+
+	result, error = strconv.common_parse_uint2('1a', 10, 8)
+	assert result == 1
+	assert error == 2
+
+	result, error = strconv.common_parse_uint2('12a', 10, 8)
+	assert result == 12
+	assert error == 3
+
+	result, error = strconv.common_parse_uint2('123a', 10, 8)
+	assert result == 123
+	assert error == 4
+}