EIC electron energies are not the same as ePIC MC samples

**Is your feature request related to a problem? Please describe.**
The electron beam energy being used by the EIC for simulations are different from the nominal values used for all ePIC MC samples in the order of a few percent.

5 GeV = 5.0674572870932 GeV
10 GeV = 9.7813741161107 GeV
18 GeV = 17.846262619763 GeV

While small, these differences are not insignificant. Over the drift vacuum passing the Low-Q2 taggers this results in a few mm steering offset.

The electron beam backgrounds produced by @nat93 are based on the machine simulation so use the more precise energy values. The energy-flux differences in this region are exponential so any mismatch between MC samples will significantly influence the rates and fraction of background electrons seen by the taggers

Recently @nat93 has showed the synchrotron sample shouldn't be effected much. The Touschek, Bremstrahlung and Coulomb samples however will need some consideration.

The same may be applicable to the ion beams.

**Describe the solution you'd like**
I don't have a preferred solution at the moment.

**Describe alternatives you've considered**
Some short and longer term solutions.

- Run background MC samples with the magnet strengths scaled appropriately and mix them afterwards
- Scale the energy of the background MC sample, either as a pre-processing stage before merging, or option when running a simulation.
- Recreate all of the MC samples with the corrected EIC energies and advise any future samples to use them too.
- Recreate the background files with the nominal 5/10/18 GeV energies.