Add inner loop aggregation options

[JamesAllingham]

Fixes #8.

This PR introduces an aggregation option for the inner_loop callback, which controls how the logs from the inner loop are aggregated. The default behavior of returning the last value for each entry in a collection is maintained. This is equivalent to manually setting aggregation="last".

aggregation supports a string value, one of "last", "first", "min", "max", "mean", and "sum" or a Callable. In this case, all values in all collections will be aggregated as specified. However, since some collections might require different aggregations (e.g., "stateful_metrics" and "metrics" likely want "last" and "mean", respectively) it is also possible to specify a dict from collection to aggregation such as {"stateful_metrics": "last", "metrics": "mean"}. If a collection is not specified in this dictionary, then the "last" aggregation is used.

A inner_loop_kwargs argument has been added to train_loop in order to surface the aggregation options to a user of that API.

The PR also adds tests for both aggregation and inner_loop_kwargs.

Let me know what you think :) I also wasn't sure how best to document this functionality.

[cgarciae]

Nice!

[cgarciae]

Thanks @JamesAllingham for doing this! I like the approach of transposing as it makes implementing reduction fairly easy.
I do have some request though, can you make it more general by also accepting Callables?

[codecov]

Codecov Report

Merging #9 (c441c0f) into main (ce3a24e) will increase coverage by 0.48%.
Report is 3 commits behind head on main.
The diff coverage is 93.02%.

@@            Coverage Diff             @@
##             main       #9      +/-   ##
==========================================
+ Coverage   77.90%   78.39%   +0.48%     
==========================================
  Files          12       12              
  Lines        1539     1578      +39     
==========================================
+ Hits         1199     1237      +38     
- Misses        340      341       +1     

Files Changed	Coverage Δ
ciclo/callbacks.py	63.69% <92.50%> (+3.92%)	⬆️
ciclo/__init__.py	100.00% <100.00%> (ø)
ciclo/loops/common.py	69.49% <100.00%> (+2.25%)	⬆️

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[JamesAllingham]

Thanks @JamesAllingham for doing this! I like the approach of transposing as it makes implementing reduction fairly easy. I do have some request though, can you make it more general by also accepting Callables?

No problem! Happy to contribute to this library. Thanks for the positive feedback.

That's a great idea – done. Let me know what you think of the changes.

[cgarciae]

Thanks!

[JamesAllingham]

My pleasure! Thanks for fixing the pre-commit.

[cgarciae]

Thanks @JamesAllingham for doing this!
Gave the PR a little push to pass it over the line.