Replace lazy_static with std::sync::OnceLock

[serprex]

once_cell is preferred over lazy_static: rust-lang-nursery/lazy-static.rs#214

[jxs]

Hi, and thanks for this! I think we can even use OnceCell or OnceLock as they have been added to std and drop any external dependency for this, wdyt?

[serprex]

Given your MSRV policy, that works. It'll also be a much more impacting change, I'm thinking RE will be made private & a function will return reference to shared regex. In the case of runner.rs that's already almost done with file_match_re

[serprex]

Reading more closely, one of the REs were unused. For finding migration files there's now a match to decide whether to construct regex for rs or sql|rs. I imagine this isn't a case where constructing regex needs to be optimized so much, otherwise the two regexen could have their own OnceLock which the match would select & no format would be involved

[jxs]

Thanks! ❤️