generic-data-functions to-dos

type-level parser names. Raw?... bad but idk what to use
add tests (steal some from binrep?)
provide a different traverse that inspects field names, to eventually replicate Gabriella's optparse-generic
- (actually I don't think we can make this a reusable generic. but we could do cool stuff with Symparsec!)
provide more versions: binary, cereal, store-style

Code quality

refactor GTraverse typevar names (not sending whole meta now, just Symbol)
highly granular constraints nice for writing, perhaps worse for type errors?
use Tagged instead of newtype spam for via?

Design points

Stuff constraints into implementation enumerators instead of use sites

Idk. I like how it is, but it's certainly messy.

GHC 9.10: Use explicit types (`RequiredTypeArguments`)

Will be a while until GHC 9.10 is stable for NixOS, so long-term task.