meta,opam,csv,sexp,toml: migrate Error/Context/Path to new Loc shape
Every codec library now:
- aliases [type t = Loc.Error.t = { ctx; meta; kind }] so consumers can
destructure with [Error.Error { ctx; meta; kind }] patterns
- takes [~ctx] / [~meta] labelled args on v / msg / raise
- drops the library-local Context sub-module in favour of the top-level
Loc.Context
- flattens error.context via Loc.Context.frames (root-to-leaf
(sort, step) pairs), with wildcard arms for the extensible Path.step
Meta: meta_error.{ml,mli} -> error.{ml,mli}, Meta_error -> Error across
lib and tests; the public module remains [Meta.Error].
Opam, CSV, TOML, Sexp: test helpers use the new Context.frames accessor
+ extensible-step wildcard (|_ -> "?"). The CSV Json.Error.to_string
leak (legacy copy-paste) dropped in favour of raw string error.