Asynchronous pruning for RubyThreadPoolExecutor #596

Job	Run time
Test without C extension	3m 15s
Test isolated (ruby)	3m 35s
Test isolated (2.3)	3m 54s
Tests: Ruby 2.3 - ubuntu	3m 25s
Tests: Ruby 2.4 - ubuntu	3m 29s
Tests: Ruby 3.0 - ubuntu	3m 16s
Tests: Ruby 2.6 - ubuntu	3m 35s
Tests: Ruby 3.4 - ubuntu	3m 17s
Tests: Ruby 2.5 - ubuntu	3m 26s
Tests: Ruby 2.7 - ubuntu	3m 28s
Tests: Ruby 3.2 - ubuntu	3m 16s
Tests: Ruby 3.1 - ubuntu	3m 17s
Tests: Ruby 3.3 - ubuntu	3m 15s
Tests: Ruby truffleruby - ubuntu	4m 14s
Tests: Ruby ruby - windows	4m 0s
Tests: Ruby jruby - ubuntu	4m 13s
	56m 55s

Provide feedback