Should AppliedFragment Monoid use spaces?

When combining AppliedFragments, should we intercalcate a space? I think technically that would violate the Monoid rules but I think that is what callers would want 99% of the time.

  /** `AppliedFragment` is a monoid. */
  implicit val MonoidAppFragment: Monoid[AppliedFragment] =
    new Monoid[AppliedFragment] {
      def combine(x: AppliedFragment, y: AppliedFragment): AppliedFragment = x |+| y
      def empty: AppliedFragment = AppliedFragment.empty
    }

Start with the AppliedFragment MonoidAppFragment definition shown in the issue and inspect the callers that combine AppliedFragments. Evaluate whether inserting spaces preserves the intended monoid behavior and matches caller expectations. Done requires a maintainer decision on the semantics, followed by an agreed implementation or documentation of the chosen behavior.