fix(NODE-4533): session support error message and unified test runner

[dariakp]

Description

NODE-4533 for NODE-4325

What is changing?

• Fixed error checking in the unified runner and the discovered non-spec compliant error message for snapshot sessions (we were skipping error checks entirely whenever an expectation contained isError or isClientError)
  • There is a new check for MongoCryptError - these aren't standardized in the fle module, so it's a bit awkward, see comment for further discussion
• Fixed a bunch of TS issues in the runner, tried to standardize the null handling as much as possible
• Updated event capturing logic since we'll be adding a new event type in the subsequent work

Is there new documentation needed for these changes?

No

What is the motivation for this change?

Splitting up groundwork from the sdam-specific unified changes

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: <type>(NODE-xxxx)<!>: <description>
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[baileympearson]

Requesting changes for visibility but only two minor comments.