Compiling large libraries uses far too much RAM.

[otrho]

As noted in https://github.com/FuelLabs/sway/issues/2674#issuecomment-1233636209 when compiling large libraries with several deps in lib.sw we can use a metric tonne of RAM.

I have a feeling we're just leaking a whole lot of intermediate data structures which could be dropped between compiling each dep, but a proper investigation should be made.