mark tests which require network connectivity

[lundybernard]

Fixes: #389

• marks tests which always require network connections as 'network'
• marks tests which download cached data once as 'cached'

[lundybernard]

This draft marks all the tests which always require a network connection as 'network', and all tests which use cached downloads as 'cached'. The one exceptionally slow test which downloads weights from AWS is the only one marked as 'slow'.

I updated the default pytest behavior in pyproject.toml to skip cached, and network tests, and the make tests command to run all 3 but fail fast. There are a lot of ways to handle the new test suites, this approach just required minimal changes.

With this change:
when new users run pytest nothing will be downloaded.
Users can run the other suites with pytest -m cached, pytest -m "network and not slow" and pytest -m slow
when you run make tests it will run the fast tests, then tests which will download and cache data, and finally the slow AWS download test (if all other tests pass)

We could also provide make targets for each test suite, and update the github actions to run each suite in a separate step (or in parallel)