Fiber DRC segmentation and SD action update for downstream digitization and reconstruction

[SanghyunKo]

To ease the review process, please consider the following before opening a pull request:

• the code is sufficiently well documented (e.g. inline comments)
• the relevant README(s) were updated. See e.g. https://github.com/key4hep/k4geo/blob/main/detector/calorimeter/README.md or https://github.com/key4hep/k4geo/blob/main/FCCee/IDEA/compact/README.md
• the code is covered by tests. See https://github.com/key4hep/k4geo/blob/main/test/CMakeLists.txt
• the PR source branch has been rebased (--ff-only) to k4geo/main
• the PR does not contain any additions or modifications that do not belong to it
• The release notes below contain a succinct and comprehensive description of the changes that are sufficiently self-explanatory

BEGINRELEASENOTES

• Use the front end instead of the rear end for the default DRC calo hit position
• Added a dedicated function to calculate the rear end position of the fiber DRC cells (only needed for the DRC digitizer)
• Made the neighborhood definition of the fiber DRC configurable via a compact file
• Fixed a bug that the fiber DRC SD action did not take the full active volume of the scintillation fiber for the energy deposit

ENDRELEASENOTES

1. Currently, we're using the rear end (where the readout electronics will be located) for the calo hit position of the DRC. However, this creates an issue when it comes to the track-cluster matching because it uses the distances between the extrapolated track state and the calo hit position, which would be ~ 2m in average if we use the rear end for the calo hit position. So I made a change to use the front end for the calo hit position.
2. The previous method (returning the rear end position) has been implemented into a dedicated function of GridDRcalo_k4geo. It is needed (and only needed) for the digitizer of the DRC that estimates the pulse timing based on the distance between the step and the readout.
3. Updated the neighborhood finding function in a way that the size of the neighborhood and the switch to include both types of cells (scintillation and Cherenkov) are configurable via a compact file.
4. Fixed a bug that the previous fiber DRC SD action did not take the full active volume of the scintillation fiber for the energy deposit.

[andresailer]

Hi @BrieucF

Could you do a final review please?

[BrieucF]

why is this if needed?

[SanghyunKo]

This comes from a historical reason - this function was designed to return the position of the tower (precisely "wafer" behind the tower) rather than the individual hit position when IsSiPM returns 0.

[BrieucF]

Thanks, can you add this as an inline comment?

[SanghyunKo]

Sure, I've just done it now