Likely caused by a lack of sandboxing on Windows, causing the generated
.d.ts files to be visible to svelte_check, and being picked up in
preference over the .svelte file.
Just a quick hack for now to store it in memory, as the temp file
conflicts on Windows due to the lack of a sandbox, and we don't really
have a need to write it to the filesystem anyway.
based on changes from upstream rules_svelte
Their code was using run_node() instead of ctx.actions.run(), which
seems to create a new worker for every CPU core, instead of respecting
the standard limit of 4.
