.circleci: Set up CircleCI

[tomtseng]

Changes

infra:

• Replaces Github Actions CI with CircleCI
• Makes CircleCI work: runs lint, runs smoke tests
  • And on every commit to main, runs multi-GPU tests through Runpod.
    • failed multi-GPU tests are supposed to notify to Slack, I haven't set that up yet though, I'll deal with it in a separate PR
• Move dev dependencies from [project.optional-dependencies] to [dependency-groups], seems to be best practices for uv

tests:

• Turns most tests into pytest tests, but adds the marker expensive and doesn't run them in CI because they're too expensive for smoke tests
• Adds one CPU integration test test test_lora_finetune_cheap (uses pythia-14m)
  • needed to refactor LoRA target_modules to not be hardcoded
• Adds one multi-GPU test
• changes the strongREJECT test to be cheaper so that it can be a CircleCI evaluation integration test

fixes:

• need to use_fast=True, the slow tokenizer had an import error. not sure if this breaks other stuff
• was having an annoyance where run_in_isolation() hangs if ctrl-C'ed, so I adjusted it to stop hanging
• fix a circular import in GCG by moving implementation from attacks/ to evals/

Testing

CircleCI passes, including multi-GPU tests

[tomtseng]

This probably deserves review but I'm going to merge to avoid adding to the backlog of PR review, and to get CircleCI passing