WIP: iron out swap integration in kernel

[bunnie]

This is the branch for working out swap integration into the kernel. A provisional to-do list includes:

• [ ] Rework argument setup from loader-to-kernel handoff, now that we know what the actual structures look like
• [ ] Rework RPT hand-off to the swapper PID
• [ ] Add baseline code to handle an actual swap event inside xous-swapper (eg WriteToSwap, ReadFromSwap) (for Precursor test case)
• [ ] Add baseline code to handle an actual swap event inside xous-swapper (for Cramium target)
• [ ] Add LRU aging (e.g. AllocateAdvisory handler + EvictPage call)
• [ ] Update documentation in Xous Book to match the reality of what was implemented
• [ ] Benchmark AES-GCM-SIV vs ChachaPoly for AEAD (optional)