ENH: add support to read, write, list and remove /vsimem/ files

[theroggy]

Add support for the basic operations on /vsimem/ files: read, write, list and remove.

TODO:

• maybe add some examples in the manual? -> DOC: Add docs for working with in-memory datasets #477
• remove pyproj again from ci/envs/latest.yml

Triggered by a topic in the "discussion" section of geopandas, where someone noted that pre-geopandas 1.0 this worked and now it does not anymore: geopandas/geopandas#3376

<-- clarified below
I now noticed the following statement in: #407

This also adds a specific check that the incoming path does not already contain /vsimem/, since we have to handle that internally and cannot allow it to be passed in.

@brendan-ward I wonder... is this meant as:

• an explicit choice not ever to want to allow /vsimem/ inputs because ???
• or a temporary measure till support has been built in
• or is there some technical reason that this causes problems that I didn't think about/haven't encountered yet

-->

[brendan-ward]

a temporary measure till support has been built in

Most likely this, though probably wasn't going to prioritize fixing it unless there was a need (apparently there is).

[brendan-ward]

Thanks for working on this @theroggy and apologies for the slow review! I only had a chance to review up to your tests and will try to review those in the next couple of days.

[brendan-ward]

A few more comments, thanks for the updates so far @theroggy , and thanks for your patience with the review.

[jorisvandenbossche]

Great work!

[brendan-ward]

I think it can be done in a later PR (but preferably for 0.10.0), but we should probably document how the /vsimem interface can be used more directly (e.g., alongside gdal package) as well as the VSI functions that we want to expose publicly here (which is why I think it is should be follow-up, so that this PR focuses on the API).

[brendan-ward]

Thanks @theroggy ! @jorisvandenbossche any final comments or disagreement with the plan to add the vsi_* functions at the top-level for now?