sort: trim unused helpers across encoding libs
Expose only what's actually called. kinded' / or_kind were added
speculatively across libraries that don't use them; revert.
- toml, xml, csv: keep to_string, pp, kinded (kinded has callers —
csv 3, toml 2, xml 1). Drop kinded' and or_kind.
- cbor, protobuf: keep to_string, pp only. Drop kinded, kinded',
or_kind (no callers).
- json keeps the full API — 38 callers including kinded' (16) and
or_kind (11).