A separate crate for common types such DataType and Value

A lot of times when using/implementing an ORM there is a lot of enum matching which DataType should be matching to essentially the same data type for the ORM implementation which ultimately maps to the underlying database DataType. There would be also conversion of Value to and fro ORM enum Value. If we can move these common types into a thin shared crate, it would remove a lot of conversion code. One example where is this applied is the `http` crate which is used in `hyper`,`actix`,and `reqwest`

该 issue 提到了 DataType 和 Value，但没有指出文件或测试。首先定位它们的定义以及 ORM/数据库转换路径，然后定义共享 crate 的边界；当公共类型可以在不重复转换的情况下复用时，这项工作就完成了。

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