Fix muon bremsstrahlung energy limits and sampling

[amandalund]

This fixes a few things in the muon bremsstrahlung interactor:

• Remove erroneous min/max model energy limits
• Add cutoff energy to interactor
• Add missing minimum cutoff energy limit
• Fix sampling of the gamma energy

I also slightly modified the brems final state helper so we can use it for this interactor too.

[whokion]

Nice fix and update! Just a couple of comments for future physics validations - may be it is a good time to add/run @stognini's validation suite for muon processes too.

[sethrj]

Follow-on to #257 and #1309 :)

[sethrj]

Only error I see is the subtle one about the RNG; please feel free to merge once that's fixed!

[sethrj]

Ooh this can't be done reproducibly. There was once a hard to track discrepancy in our CI between intel/gcc because intel would sample one function first and GCC would sample the other.

[amandalund]

Ah, I thought because I used brace initialization here they would always be sampled in the order they appear?

[sethrj]

I think that's only true for initializer lists, not constructor arguments... could be wrong though!

[amandalund]

From the standard:

4 Within the initializer-list of a braced-init-list, the initializer-clauses, including any that result from pack
expansions (14.5.3), are evaluated in the order in which they appear. That is, every value computation and
side effect associated with a given initializer-clause is sequenced before every value computation and side
effect associated with any initializer-clause that follows it in the comma-separated list of the initializer-list.
[ Note: This evaluation ordering holds regardless of the semantics of the initialization; for example, it applies
when the elements of the initializer-list are interpreted as arguments of a constructor call, even though
ordinarily there are no sequencing constraints on the arguments of a call. -- end note ]

So from the note it sounds like it should be true (I initially did make this mistake, but caught it when the SB and RB tests started failing).

[sethrj]

Wow, that's a deep cut. Good find! Hopefully the compilers all follow this standard 😅