feat: handle malformed responses from Gemini

[vsoch]

Changes:

• In getting MPI tracebacks, Gemini gets a malformed response error. This is likely because of the extra characters in the traceback, so we need to clean the output for these cases.
• I created a simple memory database backend that will store events (e.g., calls, steps, timings) and metrics (e.g., tokens) instead of the metadata dictionaries we were carrying around on each class. The database interface can be extended to handle sqlalchemy types, but this is simple enough to start. Examples: