Detect number of cores

Problem to Solve

Right now Iridium is single-threaded, with the exception of using the REPL where you can spawn background tasks. If we want to allow true parallelism with any higher abstractions, we need to support this.

Proposal

As a first step towards co-routines and allowing true parallelism, we should add in detecting the number of cores when an Iridium VM starts up and saving that info somewhere

We should also allow number of OS threads to be set from the CLI