Refactor syscall handler and add FileList, CreateDir, Version syscalls

[BogdanUser404]

I have performed a small refactoring of the syscall dispatcher by replacing the constants in number.rs with a type-safe

• SyscallCode enum. I also renamed the variable n to syscall_code for better clarity.
• Added 3 new system calls:
• Version: Returns a packed version ID.
• CreateDir: Creates a directory at the specified path.
• FileList: Populates a provided buffer with the list of file names and returns the number of entries.

This is one of my first Pull Requests to this project. I've also updated the Makefile to allow testing on different CPU architectures and memory configurations.