Check GENIE interaction time and adjust BNB bunch timing to agree with other measurements

[jzettle]

Want to change the BNB bunch structure in our BNB generator to 18.936 ns following MicroBooNE's paper: https://arxiv.org/abs/2304.02076 and the ICARUS studies which agree with this. There is a corresponding SBND PR here that makes this change: SBNSoftware/sbndcode#419

[PetrilloAtWork]

It would be good to have in sbncode a common source for this parameter (and maybe for most of BNB@GENIE configuration).

[jzettle]

I agree @PetrilloAtWork. The only reason I didn't say that was I wasn't sure how we wanted to handle that moving forward. We can think to use this as a test case for the idea of moving common SBND/ICARUS fcl parameters to sbncode if we think that is a good idea.

[jzettle]

I have added the idea to confirm the GENIE interaction time works as we expect. From looking at a test sample I made recently we thought further checking was needed as we did not see the correlation between position and time that we expected