Re: [PATCH RFC 4/4] gpu: nova-core: gsp: convert GspMem to zerocopy via the transmute bridge

This is pre-existing and not changed by this patch: it only makes
explicit (via a checked `zerocopy` derive) what the previous `unsafe
impl transmute::{FromBytes, AsBytes}` already allowed implicitly -- the
layout is byte-identical and the message-handling path is untouched -- so
it neither introduces nor addresses this. I'm not familiar enough with
the GSP threat model to judge whether the TOCTOU is in scope here; if it
is worth noting, I can add a TODO comment near the affected reads.