refactor: Move clusterization functions to core

[gagnonlg]

Move the clusterization function from the Digitization plugin to core. At the same time, change the cell energy field to activation, and the energy cut to a threshold instead to make the semantic more generally applicable than only at digitization level. Also add a static concept check on the cell type.

This does not change the public API, but since we plan to use this function in Athena this may need to fall under semver at some point in the future.

cc @asalzburger

[codecov]

Codecov Report

Merging #858 (a5c720a) into main (4c6c00a) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #858      +/-   ##
==========================================
+ Coverage   48.65%   48.70%   +0.04%     
==========================================
  Files         330      331       +1     
  Lines       17076    17115      +39     
  Branches     8053     8075      +22     
==========================================
+ Hits         8309     8336      +27     
  Misses       3089     3089              
- Partials     5678     5690      +12     

Impacted Files	Coverage Δ
...ore/include/Acts/Clusterization/Clusterization.ipp	69.23% <100.00%> (ø)

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[asalzburger]

Looks good - we should probably also see what we do with the SparseCCL algorithm in the future.