Make spawnulator a service

[jamesmunns]

This PR moves the spawnulator into a kernel service, allowing for potentially
"non-hierarchical" forth instances (e.g. a tid0 gui and tid1 sermux instance) to
use the same spawnulator.

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[jamesmunns]

There is a slight footgun, in that it is possible to try to spawn forth tasks without
having spawned the spawnulator, which I did run into during testing.

Open to suggestions on how to fix this, including maybe lazily/racily spawning the spawnulator instead of doing the normal "wait until the server appears" behavior.

[hawkw]

always be spawnulating

[jamesmunns]

There is a slight footgun, in that it is possible to try to spawn forth tasks without
having spawned the spawnulator, which I did run into during testing.

I ran into this again while developing #110, which means I should definitely fix it.

[hawkw]

There is a slight footgun, in that it is possible to try to spawn forth tasks without

having spawned the spawnulator, which I did run into during testing.

I ran into this again while developing #110, which means I should definitely fix it.

maybe we could have an atomic flag that gets set when the spawnulator is spawnulated? and check that every time we spawn a forth task. minor overhead but it's probably fine.