refactor!: Store unsigned 64bit integer for projector in MTJ backend

[paulgessinger]

Is this breaking?

[codecov]

Codecov Report

Merging #1958 (c838a7c) into main (d2882c8) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main    #1958      +/-   ##
==========================================
- Coverage   49.60%   49.60%   -0.01%     
==========================================
  Files         410      410              
  Lines       23297    23298       +1     
  Branches    10630    10631       +1     
==========================================
  Hits        11557    11557              
  Misses       4292     4292              
- Partials     7448     7449       +1     

Impacted Files	Coverage Δ
Core/include/Acts/EventData/MultiTrajectory.hpp	71.12% <50.00%> (+0.07%)	⬆️

... and 1 file with indirect coverage changes

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[github-actions]

📊 Physics performance monitoring for c838a7c

Full report
Seeding: seeded, truth estimated, orthogonal
CKF: seeded, truth smeared, truth estimated, orthogonal
IVF: 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

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

[benjaminhuth]

I would argue not, because this looks like an implementation detail to me. Is there a reason why the typedef is not in the detail namespace?

[paulgessinger]

I guess it could be, as the "public public" interface is independent of how it's stored, but the "private public" interface (the one the backends are built against) does require this to be known. I don't know, honestly.

[tboldagh]

Definitely ok from perspective of other ATLAS backend.
Side comment. I realised that probably calling these backend classes: *Backend would relay help in understanding the code.