Fix generatedNodes benchmark bug

[EliasLF]

Description

Fixing a minor bug, where sometimes the number of generated nodes is undercounted in the benchmark because nodes with equivalent layout are not added multiple times to the priority queue. Therefore, instead of relying on the size of the priority queue, it is more stable to rely on the node ids, which are strictly incremented for each generated node.

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6d17373) 93.0% compared to head (f84ee5c) 93.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #411     +/-   ##
=======================================
- Coverage   93.0%   93.0%   -0.1%     
=======================================
  Files         46      46             
  Lines       4946    4944      -2     
  Branches     852     852             
=======================================
- Hits        4604    4602      -2     
  Misses       342     342             

Flag	Coverage Δ
cpp	92.7% <100.0%> (-0.1%)	⬇️
python	96.0% <ø> (ø)

Files	Coverage Δ
src/heuristic/HeuristicMapper.cpp	94.1% <100.0%> (-0.1%)	⬇️

... and 1 file with indirect coverage changes

[burgholzer]

LGTM