Tracking issue: remaining work for full 4D tracking support

[jburzy]

This issue tracks the remaining steps towards full 4D tracking support in CKFTrackingAlg for #72.

1. Per-hit time errors from EDM4hep

The per-sensor resolutions currently have to be configured by hand, mirroring the digitizer's ResolutionT settings. The clean solution is to persist the resolution in the data:

• EDM4hep: add a timeError [ns] member to the tracker hit types and the TrackerHit interface (schema version bump; scalar, mirroring du/dv and eDepError — time smearing is uncorrelated with position, so no extension of the position covariance is needed)
• k4Reco DDPlanarDigi: setTimeError(resT) with the per-layer resolution actually used for smearing
• CKFTrackingAlg: prefer hit.getTimeError() when > 0, fall back to the HitTimeResolutionCellIDs configuration for files predating the schema change

(Implementations for all three exist and are compile-tested; blocked on the EDM4hep schema change propagating through a release and the key4hep stack.)

2. Digitizer time-convention migration

DDPlanarDigi historically subtracted the propagation TOF from stored hit times. With MuonColliderSoft/k4Reco#17 the TOF correction can be applied to the time-window cut only, keeping absolute stored times, which is what the 4D fit wants.

• Once samples are produced with the new digitizer flags, drop HitTimesCorrectedForPropagation=True from configurations
• Longer term: consider removing the add-back path entirely once no TOF-corrected samples remain in use.

3. Seeding

• Seed track parameters: the seed time is taken from the bottom space point with a configurable initial variance — estimate the seed time (and its error) from all three space points instead
• Smarter usage of SP triplet times in seed filter.

4. Validation & tests

• Verify the fitted track time reaches the edm4hep TrackState (AtIP) correctly and add a pull/resolution check
• Add a 4D configuration to the MAIA CTest chain (the test digitizers already smear times with ResolutionT), covering UseHitTimeInCKF, the per-sensor resolution configuration, and the failure modes (missing/incomplete HitTimeResolutionCellIDs)
• Physics validation with full BIB: efficiency/fake-rate/CPU versus the 3D configuration (first results: 4D CKF adds ~10% CPU on top of the branch-stopper configuration with comparable efficiency)

[madbaron]

Just to mention it here that if you develop the edm4hep update in a fork, we can collect all packages in branch of https://github.com/MuonColliderSoft/mucoll-spack for coherent testing