Fix: CLI Windows Write exe Errors

[DogeDark]

The CLI fails to write the new executable on Windows because the old one is still running during rebuilds.

This PR introduces a kill_all() method on the AppRunner. Ideally, the app would be killed right before the bundler starts, but I wasn't sure how to best get a handle down to the bundler. Instead, I opted for this simpler, but perhaps slightly less DX solution (since the app is closed during rebuilds and the dev can't admire their desktop app or interact with serverfns).

[jkelleyrtp]

This is good for now, but a better solution to this problem might be:

• to write the executables with a hash attached to the name that we save in the BuildArtifacts that gets removed
• split apart build and bundle into two separate phases that only kills when we start bundling

When builds take a while it is nice to still have the app interactive. Hopefully one day our binary patching is good enough for most cases though.

It might be worth it to gate the killall only on windows since mac/linux seem okay (and I think technically end up doing hotreloading automatically...)

[DogeDark]

@jkelleyrtp If it sounds good to you, I will gate this behind Windows and I'll add the preferred fix into Notion for a future patch release so that it's ready for 0.6, but can be properly fixed when there is more time.