hub-client: [process] fix "passes CI but doesn't work"

[cscheid]

#78 passes CI but doesn't actually work. We should try to get to the bottom of this so we can rely on the green light from GHA.

[gordonwoodhull]

This turns out to have multiple causes:

• we need to discover _extensions/ files
• we were running tests against the native Lua API, not the restricted Lua API available in the browser
  • and didn’t have smoke-all tests exercising modules like os and io
  • and need to implement those modules for the restricted API
• … probably more

So this has a lot of mundane and expected reasons, which should be addressed in that PR.