refactor: move extensions to their own packages

[gadomski]

This is a proposed refactor of each extension into its own Python package. Basic idea goes like this:

• Change the main Python package to be named pystac-core, but keep the code and import paths the same
• Move each extension to its own Python package
• Create a "meta" package named pystac that depends on everything
• Create a custom pytest plugin so we can share config among all the packages
• Relax our coverage expectation to 70%, and only run coverage on the core code (not extensions)

This should keep the install story and API identical, while simultaneously de-coupling our extension versions from our main PySTAC version.

Opening as a draft to get a smell check on the idea.

Note

I've disabled the benchmark CI for the time being to get things green, as asv is cranky with the new setup.

[jsignell]

Whoa. I love it 😍

The only part that is hitting me a little weird is that the extension logic is nested under pystac/extensions. Aside from that looking a little odd I am also wondering if there is a risk of a conflicting file existing in pystac core.

[gadomski]

The only part that is hitting me a little weird is that the extension logic is nested under pystac/extensions. Aside from that looking a little odd I am also wondering if there is a risk of a conflicting file existing in pystac core.

Yeah, it's a good point, though if we move those files (base.py, ext.py, and hooks.py) it'll be a breaking API change? Maybe we move them out of pystac/extensions when we do v2.0?

[gadomski]

Just for sake of example, the latest release-please PR (#1632) is a good illustration of why splitting extensions is good:

I don't think the storage extension should bump our MINOR.

[jsignell]

This looks great! Just a few little comments