Optional progress bar for intensive incremental operations

首先跟踪 cfa 使用的聚合路径以及相应的交互式 Python 入口点；该 issue 未列出任何文件或测试。确定进度条、spinner 或计数器的范围以及全局配置的行为，然后验证这些入口点中默认启用和禁用的情况。

For select operations that may take a non-negligible time to complete (from the perspective of a user), it could be useful to display small indicators of the progression of the operation whilst it is running in either interactive Python or on the command-line (i.e. for cfa, since aggregation is one of the main operations I have in mind that can necessarily be time-consuming for specifically inputs).

Notably, this could be:

• a progress bar for operations that can be broken into incremental steps of progression, e.g. each of the known and registered numbers of iterations through a core loop;
• perhaps a spinner or counter in the case that there is no simple or accurate way to indicate a proportion of progress having been made;

so that the user can know roughly how long they can expect or wait for the completion, or in the latter case at least see visually and be more confident that the operation hasn't stalled.

(As we have seen, Dask has a similar feature for diagnostics etc.:

)

There may be some users that don't want this feature so I suggest we have a global configuration option to disable it, but enable by default.

Implementation options

It wouldn't be difficult to code up a primitive progress bar and spinner, but for something available out-of-the-box and with more options and support, I think it would be better to use a dedicated progress bar library.

There are various such options for Python (there's a good summary here) but I think tqdm seems the best choice at the present time for features, low overhead, support available etc.