Add CapbilityPtr and Add SuccessAddr and SuccessPtr syscall variants

[LawrenceEsswood]

Pull Request Overview

This changes some u32s into usizes as appropriate.

It also introduces a new MetaPtr type that is a pointer that has explicit target dependant metadata. On many platforms, this will just be a wrapper around usize. On CHERI platforms MetaPtr will be a capability.
See later commit.

It also adds a new syscall encoding encode_syscall_return_metaptr That is intended to work for both 32/64 platforms with or without this extra metadata.

Testing Strategy

Running on QEMU

TODO or Help Wanted

This pull request still needs review, especially around encode_syscall_return_mptr which makes some decisions on how 64-bit syscalls should work

Documentation Updated

None

Formatting

• [x ] Ran make prepush.