serializedConfigToString now asks a control-located config instance
whether each field is readable and writable instead of relying on a
hard-coded list per command. Hidden and unknown fields are skipped, and
field descriptions are written as comments above each value.
Object fields such as factorio.settings are now included, so they are
written as JSON, and configToKeyVal splits on the first = only so those
values survive the round trip.
Fixes#1051
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
