Update poetry groups

[samamorgan]

Updating poetry groups to address the currently failing CI.

• Adds test group for test-only dependencies
• Makes all extra groups optional
  • Note: With this change, developers will need to run poetry install --with dev,test to get all the necessary packages for a working environment.
• Adds tomli to docs dependencies (It's used directly in our source, but was a secondary dependency of Black)

[samamorgan]

@gone Merging without review, this is holding up other PRs.