Feat: --cutoff and "keep_workspace_files" options

[lc0rp]

Background

• When creating, debugging or fixing tests or agents' performance on tests, it'd be helpful to have an option between the configured data.cutoff, and --nc.
• Similarly, it's sometimes useful to prevent workspace destruction, when debugging failing tests.

Changes

• Added --cutoff (seconds) so you can override the cutoff time from commandline
• Added a "keep_workspace_files" config option to prevent workspace teardown after tests

PR Quality Checklist

• I have run the following commands against my code to ensure it passes our linters:

  black . --exclude test.py
  isort .
  mypy .
  autoflake --remove-all-unused-imports --recursive --ignore-init-module-imports --ignore-pass-after-docstring --in-place agbenchmark

==> Mypy had a few notes, unrelated to this code. I'm happy to help look at them later.