Faster comparisons for priority queue

[brian-pane]

No description provided.

[brian-pane]

The CI errors look like a compiler crash. I don't think the problem is due to this PR itself, but I've only had a very brief look at the error messages.

Anyway, this change improves the CPU cycles at compression levels 1-7 on my test system, with the biggest improvement at level 2:

Benchmark 1 (42 runs): ./blogpost-compress-baseline-native 2 rs silesia-small.tar
  measurement          mean ± σ            min … max           outliers         delta
  wall_time           122ms ±  823us     121ms …  126ms          1 ( 2%)        0%
  peak_rss           24.9MB ± 58.3KB    24.9MB … 25.0MB          0 ( 0%)        0%
  cpu_cycles          496M  ±  758K      495M  …  497M           0 ( 0%)        0%
  instructions       1.06G  ±  323      1.06G  … 1.06G           0 ( 0%)        0%
  cache_references    270K  ± 11.1K      265K  …  338K           2 ( 5%)        0%
  cache_misses        236K  ± 3.79K      215K  …  243K           3 ( 7%)        0%
  branch_misses      6.83M  ± 8.75K     6.82M  … 6.86M           0 ( 0%)        0%
Benchmark 2 (43 runs): ./target/release/examples/blogpost-compress 2 rs silesia-small.tar
  measurement          mean ± σ            min … max           outliers         delta
  wall_time           118ms ± 1.23ms     117ms …  123ms          4 ( 9%)        ⚡-  2.9% ±  0.4%
  peak_rss           24.9MB ± 57.9KB    24.9MB … 25.0MB          0 ( 0%)          -  0.0% ±  0.1%
  cpu_cycles          480M  ± 2.60M      478M  …  496M           1 ( 2%)        ⚡-  3.2% ±  0.2%
  instructions       1.05G  ±  278      1.05G  … 1.05G           3 ( 7%)          -  0.5% ±  0.0%
  cache_references    270K  ± 6.78K      264K  …  293K           6 (14%)          -  0.3% ±  1.5%
  cache_misses        236K  ± 7.55K      210K  …  246K           3 ( 7%)          +  0.2% ±  1.1%
  branch_misses      6.20M  ± 4.66K     6.19M  … 6.21M           0 ( 0%)        ⚡-  9.3% ±  0.0%

[folkertdev]

The CI problems are due to a bug in the nightly rust version. Should sort itself out overnight.

These results look awesome, great find! I even get some decent improvements for level 9