[BUG] Script preloading ignores stitches

[PhoebeMitchell]

Describe the bug

Ink allows you to create knots which you can divert to, and these knots can contain stitches.
https://github.com/inkle/ink/blob/master/Documentation/WritingWithInk.md#6-includes-and-stitches

=== Knot
= stitch1
= stitch2

Currently the script preloading and validation reads knots correctly, but completely ignores stitches and I don't know why.
Would be nice if this feature was usable.

Steps To Reproduce

Make a script that includes a knot with stitches from another file. The stitches should contain actions like "&ACTOR:Ross"
Try and play the script.
You should get an error claiming Ross is not in the dictionary.
This is because the stitches have not been read when preloading, but when reading the script normally the stitches ARE read, but the actors have no been preloaded.

Expected behavior

Actions in stitches should be preloaded and useable without errors.