Asynchronous pruning for RubyThreadPoolExecutor #587

Job	Run time
Test without C extension	3m 13s
Test isolated (2.3)	3m 51s
Tests: Ruby 2.3 - ubuntu	6m 34s
Test isolated (ruby)	3m 39s
Tests: Ruby 2.4 - ubuntu	3m 32s
Tests: Ruby 2.5 - ubuntu	3m 28s
Tests: Ruby 2.6 - ubuntu	3m 34s
Tests: Ruby 2.7 - ubuntu	3m 29s
Tests: Ruby 3.0 - ubuntu	3m 16s
Tests: Ruby 3.1 - ubuntu	3m 19s
Tests: Ruby 3.2 - ubuntu	3m 20s
Tests: Ruby 3.3 - ubuntu	3m 15s
Tests: Ruby 3.4 - ubuntu	3m 15s
Tests: Ruby jruby - ubuntu	8m 49s
Tests: Ruby truffleruby - ubuntu	4m 12s
Tests: Ruby ruby - windows	6m 38s
	1h 7m 24s

Provide feedback