KinKal truth-seeded track extrapolation

[RobMina]

... for MC. Helps to disentangle fit uncertainty from extrapolation bias/resolution. Turned off by default, comments in prolog.fcl show how to enable it.

This is independent of the material definition PR.

[FNALbuild]

Hi @RobMina,
You have proposed changes to files in these packages:

• Mu2eKinKal

which require these tests: build.

@Mu2e/fnalbuild-users, @Mu2e/write have access to CI actions on main.

📝 The author of this pull request is not a member of the Mu2e github organisation.

About FNALbuild. Code review on Mu2e/Offline.

[brownd1978]

Hi Rob, this is a nice addition to our functionality.
I'm uncomfortable adding MC-specific code to reconstruction modules intended nominally to run on real data, as that adds an otherwise unnecessary dependency. Eventually we will need to split MC-specific codes out of Offline, and this coupling will make that harder.
An alternative is to write a dedicated module that produces a KKTrack based purely on MC information. If you need to associate that with the reco KKTrack you could do that via the KalSeedMC. What do you think?