refactor: Replace `EigenStepper` extension list with single extension

[andiwand]

Since we always only use one extension in the stepper and there are cases where it is beneficial to only worry about the state of a single extension I propose to remove the Auctioneer and the StepperExtensionList.

This came up during working on the implementation of the covariance transport where our two default extensions would have to interact via state in the EigenStepper which is rather a mess. My proposed solution would move the state consistently to the extension.

issues

• https://github.com/acts-project/acts/issues/2868

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 88.23529% with 6 lines in your changes missing coverage. Please review.

Project coverage is 48.81%. Comparing base (5893004) to head (a4b9574). Report is 584 commits behind head on main.

Files with missing lines	Patch %	Lines
Core/include/Acts/Propagator/EigenStepper.ipp	83.33%	1 Missing and 1 partial :warning:
...Acts/Propagator/detail/GenericDefaultExtension.hpp	77.77%	0 Missing and 2 partials :warning:
...agator/detail/GenericDenseEnvironmentExtension.hpp	92.85%	1 Missing :warning:
...de/Acts/Propagator/detail/GenericExtensionBase.hpp	91.66%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2865      +/-   ##
==========================================
- Coverage   48.89%   48.81%   -0.08%     
==========================================
  Files         488      487       -1     
  Lines       28253    28133     -120     
  Branches    13307    13229      -78     
==========================================
- Hits        13813    13732      -81     
- Misses       4827     4865      +38     
+ Partials     9613     9536      -77     

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[github-actions[bot]]

📊: Physics performance monitoring for 6930518237c1ca360faa508ccbc94de9be46ed9d

Full contents

physmon summary

• ✅ Particles fatras
• ✅ Particles geant4
• ✅ Particles ttbar
• ✅ Vertices ttbar
• ✅ Truth tracking (KF)
• ✅ Truth tracking (GSF)
• ✅ Truth tracking (GX2F)
• ✅ CKF | trackfinding | single muon | truth smeared seeding
• ✅ Track Summary CKF | trackfinding | single muon | truth smeared seeding
• ✅ Seeding trackfinding | single muon | truth estimated seeding
• ✅ CKF | trackfinding | single muon | truth estimated seeding
• ✅ Track Summary CKF | trackfinding | single muon | truth estimated seeding
• ✅ Seeding trackfinding | single muon | default seeding
• ✅ CKF | trackfinding | single muon | default seeding
• ✅ Track Summary CKF | trackfinding | single muon | default seeding
• ✅ Seeding trackfinding | single muon | orthogonal seeding
• ✅ CKF | trackfinding | single muon | orthogonal seeding
• ✅ Track Summary CKF | trackfinding | single muon | orthogonal seeding
• ✅ Seeding trackfinding | 4 muon x 50 vertices | default seeding
• ✅ CKF | trackfinding | 4 muon x 50 vertices | default seeding
• ✅ Track Summary CKF | trackfinding | 4 muon x 50 vertices | default seeding
• ✅ Ambisolver | trackfinding | 4 muon x 50 vertices | default seeding
• ✅ IVF notime | trackfinding | 4 muon x 50 vertices | default seeding
• ✅ AMVF gauss notime | trackfinding | 4 muon x 50 vertices | default seeding
• ✅ AMVF grid time | trackfinding | 4 muon x 50 vertices | default seeding
• ✅ Seeding trackfinding | ttbar with 200 pileup | default seeding
• ✅ CKF | trackfinding | ttbar with 200 pileup | default seeding
• ✅ Track Summary CKF | trackfinding | ttbar with 200 pileup | default seeding
• ✅ Ambisolver | trackfinding | ttbar with 200 pileup | default seeding
• ✅ AMVF gauss notime | trackfinding | ttbar with 200 pileup | default seeding
• ✅ AMVF grid time | trackfinding | ttbar with 200 pileup | default seeding

[acts-project-service]

:red_circle: Athena integration test results [160b57cb67c62b80381693f8ddf30899e88c1081]

Build job with this PR failed!

Please investigate the build job for the pipeline!

[sonarqubecloud[bot]]

Quality Gate failed

Failed conditions
39.92% Line Coverage on New Code (required ≥ 50%)

See analysis details on SonarCloud