feat: enable geantino particle generation

[andiwand]

Allows shooting geantino particles into the detector with our particle gun

Example gun:

addParticleGun(
    s,
    ParticleConfig(1, acts.PdgParticle.eInvalid, randomizeCharge=False, charge=1, mass=0),
    rnd=rnd,
)

[codecov]

Codecov Report

Merging #1888 (8299f1f) into main (fffb998) will not change coverage.
The diff coverage is n/a.

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##             main    #1888   +/-   ##
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  Coverage   49.44%   49.44%           
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  Files         408      408           
  Lines       22704    22704           
  Branches    10371    10371           
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  Hits        11226    11226           
  Misses       4266     4266           
  Partials     7212     7212           

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[github-actions]

📊 Physics performance monitoring for 8299f1f

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

[andiwand]

in principle we could drop this completely now

    /// Force pdgCode & mass & charge in G4 units (this is needed for Geantino
    /// simulation)
    std::optional<G4int> forcedPdgCode;
    std::optional<G4double> forcedCharge;  // e.g. 1 for charged geantino
    std::optional<G4double> forcedMass;    // e.g. 0 for geantino

but we still depend on it in https://github.com/acts-project/acts/blob/main/Examples/Run/Geant4/Common/src/Geant4Common.cpp#L77

[benjaminhuth]

Let's get it in!