Added helper to get single gene normalized rates

[vals]

I made a helper method for Posterior which lets you get expression rates at a normalized library size for a single gene of interest. This way you can e.g. plot the expression of a particular gene without needing to store the 'imputed' matrix for the entire dataset in RAM.

[adamgayoso]

It seems like this could all be options in the already existing get_sample_scale() method. We should also add an option that averages the value over many samples. What do you think @romain-lopez ?

[romain-lopez]

Hi Valentine,

Thanks for contributing. Indeed, I think we could refactor this to be a modification of get_sample_scale by adding some options to it!

Best,
Romain

[vals]

Sure! I'll take a stab at making a refactored version

[adamgayoso]

Thanks for the contribution @vals. Please let me know what you think.

[vals]

It seems the tool black is failing on the CI. I'm not familiar with it, do you have any guidance on how I can address it?

[adamgayoso]

@vals sorry I missed this. I'll give a review now, but perhaps upgrading your black will help fix this.

[adamgayoso]

@vals, we'd like to get 0.6.2 out soon. If you're able to address these items soon we could include this. No rush, but just wanted to keep you in the loop.

[adamgayoso]

LGTM, not sure what's happening with CI. Might have to merge into a temporary branch and make a new PR. Also I'll add a test for this.