Mark the reporter thread as "fork safe" to avoid warnings

[carlosantoniodasilva]

This prevents the Reporter thread from generating warnings with puma, which has been warning on any threads created before forking.

The Reporter thread is aware of forking by keeping the current pid around, and initializing another thread if the pid changes. It means we still have a running Reporter on the main puma process in this case, plus one for each forked process (if running in cluster mode, in case of puma.)

References:
rails/rails#40399
puma/puma#2475
https://github.com/puma/puma/releases/tag/v5.1.0

Closes #170

[carlosantoniodasilva]

Unrelated judoscale-solid_queue failure (which seems a solid_queue problem)

/home/runner/work/judoscale-ruby/judoscale-ruby/vendor/bundle/ruby/2.7.0/gems/solid_queue-0.8.2/lib/solid_queue/processes/callbacks.rb:8:in `block in <module:Callbacks>': 
uninitialized constant SolidQueue::Processes::Callbacks::ActiveModel (NameError)
Did you mean?  ActiveJob

[adamlogic]

Unrelated judoscale-solid_queue failure

Very strange, especially since it's been passing fine, and we haven't changed anything. 🤔

[adamlogic]

Thanks @carlosantoniodasilva!!

[carlosantoniodasilva]

it's been passing fine, and we haven't changed anything.

I think it's because it picked up a newer version of solid_queue and that's not requiring active model correctly.