feature: add support unsigned syntax on tianmu engine

[hustjieke]

Is your feature request related to a problem? Please describe.

mysql> create table t1( a int unsigned zerofill, b int) engine = innodb;
Query OK, 0 rows affected (0.03 sec)

mysql> create table t2( a int unsigned zerofill, b int) engine = tianmu;
ERROR 6 (HY000): UNSIGNED data types are not supported.

Describe the solution you'd like

Remove UNSIGNED_FLAG check in Engine::GetAttrTypeInfo():

  switch (field.type()) {
    case MYSQL_TYPE_SHORT:
    case MYSQL_TYPE_TINY:
    case MYSQL_TYPE_INT24:
    case MYSQL_TYPE_LONG:
    case MYSQL_TYPE_FLOAT:
    case MYSQL_TYPE_DOUBLE:
    case MYSQL_TYPE_LONGLONG:
      if (field.flags & UNSIGNED_FLAG)
        throw common::UnsupportedDataTypeException("UNSIGNED data types are not supported.");
      [[fallthrough]];

Describe alternatives you've considered

Additional context

Note:

As of MySQL 8.0.17, the UNSIGNED attribute is deprecated for columns of type [FLOAT](https://dev.mysql.com/doc/refman/8.0/en/floating-point-types.html), [DOUBLE](https://dev.mysql.com/doc/refman/8.0/en/floating-point-types.html), and [DECIMAL](https://dev.mysql.com/doc/refman/8.0/en/fixed-point-types.html) (and any synonyms); you should expect support for it to be removed in a future version of MySQL. Consider using a simple CHECK constraint instead for such columns.

The result depends on the SQL mode in effect at the time, see:
Out-of-Range and Overflow Handling
https://dev.mysql.com/doc/refman/8.0/en/out-of-range-and-overflow.html

Required Storage and Range for Integer Types Supported by MySQL:
https://dev.mysql.com/doc/refman/8.0/en/integer-types.html

[hustjieke]

Warning:
When you use subtraction between integer values where one is of type UNSIGNED, the result is unsigned unless the NO_UNSIGNED_SUBTRACTION SQL mode is enabled. See Section 12.11, “Cast Functions and Operators”.

• UNSIGNED [INTEGER]

Produces an unsigned BIGINT value.

MySQL supports arithmetic with both signed and unsigned 64-bit values. For numeric operators (such as + or -) where one of the operands is an unsigned integer, the result is unsigned by default (see Section 12.6.1, “Arithmetic Operators”). To override this, use the SIGNED or UNSIGNED cast operator to cast a value to a signed or unsigned 64-bit integer, respectively.

mysql> SELECT 1 - 2;
        -> -1
mysql> SELECT CAST(1 - 2 AS UNSIGNED);
        -> 18446744073709551615
mysql> SELECT CAST(CAST(1 - 2 AS UNSIGNED) AS SIGNED);
        -> -1
If either operand is a floating-point value, the result is a floating-point value and is not affected by the preceding rule. (In this context, [DECIMAL](https://dev.mysql.com/doc/refman/8.0/en/fixed-point-types.html) column values are regarded as floating-point values.)

mysql> SELECT CAST(1 AS UNSIGNED) - 2.0;
        -> -1.0