Add lazy version of shared_datadir

[nyoma-diamond]

A quick-and-dirty implementation of the lazy datadir that uses a shared data directory mimicking shared_datadir.

This is very useful for when there are a lot of data files and organizing them for every single test / test file instead of using a single shared data directory is very cumbersome, but copying all of the files each time shared_datadir is used induces lots of excessive copying/file usage.

[nicoddemus]

Seems reasonable, thanks @nyoma-diamond!

Could you please provide tests for the new fixture?

[nyoma-diamond]

Yup sure thing :)

[nyoma-diamond]

@nicoddemus Hopefully those tests are sufficient?

It's worth noting that I've made an explicit design choice (admittedly somewhat arbitrarily, but I think makes sense) to have lazy_shared_datadir create tmp_path / "data" upon initialization. Alternatively it may be acceptable to not create the directory explicitly and just let it be created the first time a file is requested, but I think creating it explicitly ensures minimal confusion over the behavior / order of operations, the overhead from empty directories is very small, and there should never be any situations where the user doesn't utilize the created directory (if the user doesn't want the directory, they don't need lazy_shared_datadir to begin with).

That said, if you disagree with the design choice, it's an easy change.

[gabrielcnr]

I think the presented new behaviour for lazy_shared_datadir is consistent with the existing behaviour of shared_datadir by choosing the tmp_path / 'data' as directory to be created. The creation of the directory is inexpensive, and being a temporary directory shouldn't be a big deal in terms of leaving residuals behind (even if the copies never happen). I think this is good enough. I will let @nicoddemus share his thoughts too.

[nicoddemus]

LGTM!

I will merge/release tomorrow to give others a chance to review. 👍

[nicoddemus]

1.8.0 released, thanks again @nyoma-diamond for the PR!