[wip] unpatch threading for dataset downloading

[jonathanzxu]

Problem

Tests were failing sometimes due to a "This operation would block forever" error from gevent.

Solution

We shouldn't call gevent functions in raw threads in the hub's ThreadPool, because they might not have Hubs and could throw. Instead reload the threading module to python's default, and re-patch on exit.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

Tests should pass