feat: processes and process scheduler

[mayant15]

This pull request implements a process system for BottleOS, mostly based on the Operating System Concepts book. After all initialization is done, kernel_main transfers control over to the Scheduler. This scheduler has an infinite loop that orchestrates processes.

To Test:

• Start the OS with cargo run, the Box and Rc test print statements should be in no particular order
• Run cargo test, all tests should pass

To Do:

• [x] Create a proc module and draft a minimal API
• [x] Implement process queues
• [x] Implement Process::new() to register this process
• [ ] Implement the process state machine with Scheduler::step()
• [ ] Implement a parent-child hierarchy for processes
• [ ] Implement Process::join()
• [ ] Write unit tests for processes

[mayant15]

Merging, will continue working directly on main.