Feature idea: Deduplicate defaults vs overrides in export output

I guess this is a fairly big change and only really relevant if we decide to use Controls as the basis for a new drop in editor (i.e. aiming for clean, production-ready configs rather than test-friendly verbosity).

`plotOptions` vs `series[]` is just one example. More generally, the editor currently repeats options at the override level even when they are identical to values already defined at a default level.

Idea is to, on export, strip options whose values are identical to the resolved defaults from higher up in the config hierarchy.
Example: if `plotOptions.series.color` is set, don’t include `series[i].color `unless it actually overrides it — but the same logic should apply anywhere in the API where defaults and overrides exist.

We could also expose this as an export option: clean/minimal output vs verbose output, so we keep the current behavior where it’s useful.

Why bother: cleaner configs, clearer intent (what’s default vs overridden), smaller output, and much nicer diffs since only real overrides show up.