message: chore: update extend theme to support new anatomy
diff: @@ -117,6 +117,19 @@ function mergeThemeCustomizer(
  key: string,
  object: any,
  ) {
  + // (backward compat) how the parts array should be merged
  + // The new Anatomy class returns an iterator instead of an array
  + // we need to convert it to an array using `Array.from`
  + if (key === "parts") {
  + //@ts-ignore
  + const _source = Array.from(source ?? []) as string[]
  + //@ts-ignore
  + const _override = Array.from(override ?? []) as string[]
  + const merged = _source.concat(_override)
  + // remove duplicates
  + return Array.from(new Set(merged))
  + }
  +
  if (
  (isFunction(source) || isFunction(override)) &&
  Object.prototype.hasOwnProperty.call(object, key)
  