DEV: Fix FinalDestination::Resolver race condition (#19558)

We were adding to the resolver's work queue before setting up the `@lookup` and `@parent` information. That could lead to the lookup being performed on the wrong (or `nil`) hostname. This also lead to some flakiness in specs.

lib/final_destination/resolver.rb

@@ -8,12 +8,14 @@ class FinalDestination::Resolver
       @result = nil
 
       @queue ||= Queue.new
-      @queue << ""
       ensure_lookup_thread
 
       @lookup = addr
       @parent = Thread.current
 
+      # Wakeup the worker thread
+      @queue << ""
+
       # This sleep will be interrupted by the lookup thread
       # if completed within timeout
       sleep timeout

spec/lib/final_destination/resolver_spec.rb

@@ -18,16 +18,12 @@ describe FinalDestination::Resolver do
 
     expect {
       result = FinalDestination::Resolver.lookup("sleep.example.com", timeout: 0.001)
-      # If the test gets this far, it failed
-      puts "Flaky test debug: Result was #{result.inspect}"
     }.to raise_error(Timeout::Error)
 
     start_thread_count = alive_thread_count
 
     expect {
       result = FinalDestination::Resolver.lookup("sleep.example.com", timeout: 0.001)
-      # If the test gets this far, it failed
-      puts "Flaky test debug: Result was #{result.inspect}"
     }.to raise_error(Timeout::Error)
 
     expect(alive_thread_count).to eq(start_thread_count)