implement `removecuratorstudio`

[faretek1]

Warning raised by scratchattach: failed to parse  {'datetime_created': '2026-05-03T13:04:40.000Z', 'id': 'removecuratorstudio-8994328', 'actor_id': 58743127, 'username': 'faretek1', 'type': 'removecuratorstudio', 'actor_username': 'faretek1'} error 'removecuratorstudio'

This appeared in the tests: https://github.com/TimMcCool/scratchattach/actions/runs/28143315964/job/83345035193

This appears to be an unimplemented/unhandled case in the activity handler (something like activity.py). This should not be too hard to fix.