Functionalise

[henrylay97]

Description

This is an internal PR within the team working on refactoring the timing reference frames for data, release managers can ignore. We will make a final PR once the main branch is ready.

In this PR I've refactored the frame shift module a little:

• Moved everything into the sbnd::timing namespace so we don't have to specify it for all the objects etc.
• Added functions to split up most of the produce() function and make things a little more readable.
• Created helper function for finding the closest timestamp in a vector to provided reference timestamp, as this was being done many times.
• Created helper function for formatting a uint64_t timestamp into seconds and nanoseconds for print statements, as this was also being done many times.
• I've reduced the duplication in the final logic, a lot of it was the same for beam and offbeam.
• I've made the indentation consistent and removed unused fcl parameters.
• I've added a fcl parameter (that defaults to false) for whether to produce the TTree.
• I've made sure we are using pre-defined default values and enumerations provided in the relevant sbnobj files.

This goes with SBNSoftware/sbnobj#156