As a follow-up to #2430, I realized that std::regex instantiation takes a decent chunk of time (like 500-750ms on my dev laptop). and given it does not need to exist (since it is needed only once, not for every translation unit that users Tracer), seems like a nice thing to improve.

I'm looking for advice on how to do so - basically where to put a definition in a .cc file. All of /api/ is just headers from what I can see, and so looking for guidance about that.

Thanks!