Script multithreading (and concurrency)

scripts now run on other thread(s) :D

this took a fair bit of cleanup, but it’s working.

changes

script workers

• moved script execution onto worker thread(s)
• worked on script worker concurrency
• dynamically clamp the number of active workers based on how many callbacks are actually running, so idle threads aren’t just spinning doing nothing

garbage collection

did some work on the GC as well.

• introduced external root tracking
• fixed a few issues around GC roots while getting multithreaded script execution working

cleanup

spent some time cleaning up a bunch of backend stuff while getting all of this working.

build system

updated CMake so all executables, scripts, and (project) templates are output to a single build/bin directory instead of being messy.

multithreading yay :)