feat: add q four-momentum vector

[wdconinc]

Briefly, what does this PR introduce?

This PR adds the four-momentum transfer vector.

[wdconinc]

Discussion in zoom chat:

• Can you provide the definitions of q in the case of the other methods, like DA, Sigma, eSigma? As a comment on that PR would be great.
• For SIDIS measurements, you want to define the q-vector w.r.t to the virtual photon direction.
• Yes, but how do you define this in methods that don't calculate this? E.g. https://github.com/eic/EICrecon/blob/main/src/algorithms/reco/InclusiveKinematicsESigma.cc#L85-L94. We want some invariants (Lorentz even) for the data model, such as q.dot(q) = Q2, regardless of which methods are used.
• It's clear for electron method where we explicitly calculate q, https://github.com/eic/EICrecon/blob/main/src/algorithms/reco/InclusiveKinematicsElectron.cc#L127.
• But the other methods... less clear to me.

[rseidl-rcf]

Discussion in zoom chat:

* Can you provide the definitions of q in the case of the other methods, like DA, Sigma, eSigma? As a comment on that PR would be great.

* For SIDIS measurements, you want to define the q-vector w.r.t to the virtual photon direction.

* Yes, but how do you define this in methods that don't calculate this? E.g. https://github.com/eic/EICrecon/blob/main/src/algorithms/reco/InclusiveKinematicsESigma.cc#L85-L94. We want some invariants (Lorentz even) for the data model, such as q.dot(q) = Q2, regardless of which methods are used.

* It's clear for electron method where we explicitly calculate q, https://github.com/eic/EICrecon/blob/main/src/algorithms/reco/InclusiveKinematicsElectron.cc#L127.

* But the other methods... less clear to me.

Yes, that was a little too naive by me. I need to look up how to do that for DA, and xSIGMA methods. For JB your qvector is just the sum of all hadronic final state 4-momenta minus the incoming hadron 4-momentum.

For clarification, we need to calculate angles and pt relative to the virtual photon direction (ie q vector) and z requires dot products with the q vector.