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`

該 issue 提到了 DataType 和 Value，但沒有指出檔案或測試。首先定位它們的定義以及 ORM/資料庫轉換路徑，然後定義共用 crate 的邊界；當共用型別可以在不重複轉換的情況下重複使用時，這項工作就完成了。

由索引模型根據 Issue 內容生成。