WIP: sprawling dune build fixes across packages

Fixes for:
- Xml.Value.element -> Xml.Value.t (xtce).
- Xml.Error.t to_string wrap (xtce.of_string).
- Json.to_string now plain; drop result patterns across sbom, runc, cdm,
freebox, gauth, gdocs, hap, sigstore, space, meross, stix.
- Loc.Error.t is a record now; read e.meta directly (rego, sbom).
- 'Err' submodule renamed to 'Error' in claude; update refs + test.ml suite list.
- Yaml_jsont -> Yaml_json (space-dtn, space).
- Move sw from Monitor.S.create to Monitor.S.start.
- Drop unused sw, bundle fields from Runc.Command records.
- Drop orphan Compact.rebuild in scitt.Vds; drop 'mutable' from levels (field
content is mutated via array write, not field reassignment).
- Claude Code test: Alcotest.fail e where e is Json.Error.t -> wrap with
Json.Error.to_string.
- toml.jsont dune refs had broken '... loc))' merger in many test/bin dunes.

Toml.ml/Codec.ml and ocaml-http/lib/Xtce.ml xtce have pending mli
mismatches from concurrent linter reshape.