`rustix::mm::Advice` is missing `MADV_GUARD_INSTALL` & `MADV_GUARD_REMOVE`, added in Linux 6.13

Ideally this should `rustix::mm::Advice` should not be an enum (or `madvise` should take `impl Into` where `RawAdvice` is an escape hatch for values not present in rustix).

Docs:
```
MADV_GUARD_INSTALL (since Linux 6.13)
Install a lightweight guard region into the range specified
by addr and size, causing any read or write in the range to
result in a SIGSEGV signal being raised.

MADV_GUARD_REMOVE (since Linux 6.13)
Remove any lightweight guard regions which exist in the
range specified by addr and size.
```

I may get off my ass and send out a PR. 🤷🏾‍♂️