Add more locks in update_status

[giordano]

Fix #131.

[AntonOresten]

Thanks!

[giordano]

I wish we could support Julia v1.11+, then we'd be able to use Lockable which makes using locks a lot simpler.

[giordano]

Ok, it turns out defining Lockable for Julia v1.10 wasn't much complicated, so I did that and we can use Lockable so we don't forget to acquire the lock every time it's necessary.

[maleadt]

I'm not sure this actually fixes the issue. For update_status, what about taking a snapshot of the relevant dicts at the start of the function?

  function update_status()
      running_snapshot = Base.@lock test_lock copy(running_tests)
      isempty(running_snapshot) && return

      results_snapshot = Base.@lock results_lock copy(results)
      completed = length(results_snapshot)
      total = length(tests)

      # continue using snapshots
  end

Lockable is still useful to protect wrkr.io.

See #133