Performance Improvements

• Optimise the queue again (#57)

  6.0.0 was significantly slower than 5.0.0. This restores the balance. Each of these benchmarks is run 10x times, in order to make the numbers reasonably stable for comparison.

  5.0.0 benchmark:

  limit=10
  10 promises: 1.118ms
  100 promises: 31.778ms
  1000 promises: 22.806ms
  10000 promises: 59.501ms
  100000 promises: 941.285ms
  1000000 promises: 11.569s
  limit=1000000
  10 promises: 0.177ms
  100 promises: 0.425ms
  1000 promises: 4.904ms
  10000 promises: 84.251ms
  100000 promises: 1.081s
  1000000 promises: 13.656s
  

  6.0.0 benchmark:

  limit=10
  10 promises: 1.122ms
  100 promises: 18.4ms
  1000 promises: 34.742ms
  10000 promises: 86.504ms
  100000 promises: 1.475s
  1000000 promises: 20.298s
  limit=1000000
  10 promises: 0.264ms
  100 promises: 0.424ms
  1000 promises: 5.6ms
  10000 promises: 93.45ms
  100000 promises: 1.466s
  1000000 promises: 20.109s
  

  6.0.1 benchmark:

  limit=10
  10 promises: 1.217ms
  100 promises: 4.433ms
  1000 promises: 49.928ms
  10000 promises: 67.578ms
  100000 promises: 958.481ms
  1000000 promises: 10.542s
  limit=1000000
  10 promises: 0.118ms
  100 promises: 0.424ms
  1000 promises: 4.993ms
  10000 promises: 84.649ms
  100000 promises: 1.163s
  1000000 promises: 13.297s