feat: Add thread reader to client

[Exterm1nate]

When stopping the client its thread continues working for some time. This is not a problem in production, but in tests it is. Webmock removes its stub after the test, while the thread is still working, so we sometimes receive such errors:

#<Thread:0x0000761ef6935090@LD/SSEClient /usr/local/bundle/ruby/3.1.0/gems/ld-eventsource-2.2.3/lib/ld-eventsource/client.rb:144 run> terminated with exception (report_on_exception is true):
/usr/local/bundle/ruby/3.1.0/gems/webmock-3.25.1/lib/webmock/http_lib_adapters/http_rb/webmock.rb:63:in `halt': Real HTTP connections are disabled. Unregistered request: GET http://localhost:3003/admin/v1/emails with headers {'Accept'=>'text/event-stream', 'Authorization'=>'Bearer test_key', 'Cache-Control'=>'no-cache', 'Connection'=>'close', 'Host'=>'localhost:3003', 'Last-Event-Id'=>'0', 'User-Agent'=>'ruby-eventsource'} (WebMock::NetConnectNotAllowedError)

This PR adds a reader for thread, so it can be killed after the test example.

subject(:call_method) do
  processor.start
  sleep 0.1
end

after do
  processor.connection.thread&.kill
end

[keelerm84]

@Exterm1nate thank you for raising the issue and working on this contribution.

I would prefer to not expose the thread as that's an implementation detail, and it enables a lot of misuse. I've updated the PR to add a close_and_wait method. This will block until that thread has shutdown, or some timeout period has elapsed.

Would this work for you?

[Exterm1nate]

This solution appears to work, but it has a noticeable disadvantage: tests will take longer if we wait for the last run_stream cycle to complete. It would be better if we could terminate the thread immediately without waiting.

[keelerm84]

tests will take longer if we wait for the last run_stream cycle to complete.

I wouldn't expect this to take long at all. That method should early exit when it sees we have called close. This makes me think something else is preventing the thread from exiting immediately, like a hung IO reader.

Do you have a small reproduction case I could reference to dig into this further?