feat: add lib/reflection.lua

[robbielyman]

here’s a clocked pattern recorder @dndrks and I have been kicking around for about a year now. some discussion of it exists over at #1609 . i’m not sure the discussion has fully resolved, so i’ll mark this as a draft, but if there’s interest, it would be nice to see it land soon :)

[robbielyman]

thanks very much to @sonocircuit for some thoughtful changes and additions!

one thing I took the liberty of doing is having begin_playback just call into clock.sync directly rather than launching a new clock. since the library itself only calls begin_playback within a clock, this seems innocent, but please let me know if you think things should change @dndrks @sonocircuit