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

[ds84182]

Ideally this should rustix::mm::Advice should not be an enum (or madvise should take impl Into<RawAdvice> 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. 🤷🏾‍♂️