Add PTB trigger fields to SRTrigger for SBND

[hbjamin]

Description

This PR adds PTB trigger information fields to the SRTrigger class in the StandardRecord structure, which is required for SBND trigger efficiency studies using zero bias data. HLT and LLT decoded bits and timestamps are stored in separate vectors for easier analysis.

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[fjnicolas]

Thanks for the PR @hbjamin!

My only comment is whether we can reduce the CAF footprint by declaring ptb_hlt_bit and ptb_llt_bit as unsigned short int instead of uint64_t. We are saving "decoded" HLT/LLLs IDs to the CAFs, and we only have a handful of them (<34).

[PetrilloAtWork]

Please confirm that double precision is indeed not losing needed precision in the timestamps.

I have also left a suggestion on the documentation format.

[hbjamin]

Thank you for the very important catch. I've update the timestamps to be uint64_t with units of UTC ns since epoch, and updated all sbncode accordingly.