Consider use of Astropy QTable

Astropy QTables are Tables with units enforced in them. The databases I have worked with thus far don't have units stored in them, but it may be that some will (perhaps if the data is in long-form) or that it can be added via some map.
We may want to consider adding a `.qtable` method that will return query output but do so in QTable form. The simplest implementation would probably require the user to provide a dictionary of column -> unit, but we can explore other options too.

首先定位查询输出 API，并检查当前如何表示返回的行或表。阅读 Astropy QTable 的要求，并将其与提议的 `.qtable` 方法以及列到单位的字典进行比较。当项目确定了单位映射方案，并且查询结果可以作为 QTables 返回时，即表示完成。

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