Adds CI runs that exclude optional dependencies

Suggested by @pearce8

We've had issues in the past with users not having optional dependencies. To account for that, we should add to our CI matrix so that we can run under different sets of extras. The extras we can consider are:
* `llnl-thicket`
* `llnl-thicket[extrap]`
* `llnl-thicket[plotting]`
* `llnl-thicket[vis]`
* `llnl-thicket[extrap,plotting]`
* `llnl-thicket[extrap,vis]`
* `llnl-thicket[plotting,vis]`
* `llnl-thicket[extrap,plotting,vis]`

No CI file or test is named in the issue. Start by locating the repository's CI matrix and the definitions for the listed extras, then run the existing checks for each requested dependency combination; done means all combinations are represented and pass CI.

Written by the indexing model from the issue text.