fix: Allow CKF smoothing without a target surface

[andiwand]

The current CKF implementation does not allow for smoothing without setting a target surface as this would result in a null pointer dereference. I try to fix that by handling the special case of not having a target surface.

[github-actions]

📊 Physics performance monitoring for d0740bb

Summary
Full report
Seeding: seeded, truth estimated, orthogonal
CKF: seeded, truth smeared, truth estimated, orthogonal
IVF: seeded, truth smeared, truth estimated, orthogonal
AMVF: seeded, truth smeared, truth estimated, orthogonal
Ambiguity resolution: seeded, orthogonal
Truth tracking
Truth tracking (GSF)

Vertexing

Vertexing vs. mu

IVF seeded

IVF truth_smeared

IVF truth_estimated

IVF orthogonal

AMVF seeded

AMVF truth_smeared

AMVF truth_estimated

AMVF orthogonal

Seeding

Seeding seeded

Seeding truth_estimated

Seeding orthogonal

CKF

CKF seeded

CKF truth_smeared

CKF truth_estimated

CKF orthogonal

Ambiguity resolution

seeded

Truth tracking (Kalman Filter)

Truth tracking

Truth tracking (GSF)

Truth tracking

[codecov]

Codecov Report

Merging #2317 (d0740bb) into main (5252d07) will increase coverage by 0.00%.
The diff coverage is 25.00%.

@@           Coverage Diff           @@
##             main    #2317   +/-   ##
=======================================
  Coverage   49.47%   49.47%           
=======================================
  Files         451      451           
  Lines       25482    25484    +2     
  Branches    11720    11720           
=======================================
+ Hits        12608    12609    +1     
  Misses       4582     4582           
- Partials     8292     8293    +1     

Files Changed	Coverage Δ
...de/Acts/TrackFinding/CombinatorialKalmanFilter.hpp	32.07% <25.00%> (+0.08%)	⬆️

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[noemina]

Pretty clear to me. Approving.

[acts-project-service]

✅ Athena integration test results

✅ All tests successful

status	job
🟢	run_unit_tests
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsWorkflow.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsValidateTracks.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsValidateActsCoreSpacePoints.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsValidateActsSpacePoints.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsValidateSeeds.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsValidateOrthogonalSeeds.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsValidateClusters.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsPersistifyEDM.sh
🟢	run_ci_tests: ../athena/AtlasTest/CITest/test/ActsKfRefitting.sh
🟢	run_ci_tests: python3 ../athena/Tracking/Acts/ActsGeometry/test/ActsExtrapolationAlgTest.py
🟢	run_ci_tests: python3 ../athena/Tracking/Acts/ActsGeometry/test/ActsITkTest.py
🟢	run_workflow_tests_run4_mc
🟢	run_workflow_tests_run2_mc
🟢	run_workflow_tests_run2_data
🟢	run_workflow_tests_run3_mc
🟢	run_workflow_tests_run3_data