Asynchronous pruning for RubyThreadPoolExecutor #575

Job	Run time
Test without C extension	3m 26s
Tests: Ruby 2.3 - ubuntu	4m 58s
Test isolated (2.3)	4m 6s
Tests: Ruby 2.4 - ubuntu	3m 55s
Test isolated (ruby)	3m 42s
Tests: Ruby 2.5 - ubuntu	3m 39s
Tests: Ruby 2.6 - ubuntu	3m 46s
Tests: Ruby 2.7 - ubuntu	3m 39s
Tests: Ruby 3.0 - ubuntu	3m 26s
Tests: Ruby 3.1 - ubuntu	3m 25s
Tests: Ruby 3.2 - ubuntu	3m 27s
Tests: Ruby 3.3 - ubuntu	3m 23s
Tests: Ruby 3.4 - ubuntu	3m 28s
Tests: Ruby jruby - ubuntu	7m 28s
Tests: Ruby truffleruby - ubuntu	4m 21s
Tests: Ruby ruby - windows	4m 58s
	1h 5m 7s

Provide feedback