Next MSRV bump

[tgross35]

Trixie released with rustc 1.85, so I expect a lot of crates will be increasing their MSRV in the next few weeks. I'd like to upgrade only as needed, rough list of what might be nice to have:

• 1.64: core::ffi::c_* (definitely need this)
• 1.64: workspace-level lints (meh)
• 1.65: cast_mut (this would be nice)
• 1.67: varargs for non-C extern ABIs (no known applications)
• 1.69: derive on packed structs that don't implement Copy (not overly useful for us, everything is copy)
• 1.75: byte_add (this would be nice)
• 1.75: const_maybe_uninit_zeroed (this would be nice)
• 1.77: offset_of (just lets us remove a polyfill)
• 1.77: C string literals (nothing we can't work around, not sure we even use this now)
• 1.78: cfg(target_abi = "...") (no known applications)
• 1.80: size_of, align_of in prelude (nice to have but we have our own prelude)
• 1.80: variadics without a named parameter (no known applications)
• 1.81: #[expect(...)] (want this, but it's not pressing)
• 1.82: unsafe extern blocks (neutral)
• 1.82: &raw (few small applications, addr_of! works fine)
• 1.82: nested access in offset_of! (no uses)
• 1.85: ptr::fn_addr_eq (we don't really need this as it is just for trait impls)
• 1.85: 2024 edition
• 1.92: &raw [mut|const] to union fields is now safe

[matze]

• 1.66: AsRawFd that could be implemented on pollfd to simplify interaction with tokio via AsyncFd

[tgross35]

• 1.66: AsRawFd that could be implemented on pollfd to simplify interaction with tokio via AsyncFd

That kind of trait implementation would be better suited for a wrapper crate the level above libc. E.g. nix::poll::PollFd, which implements AsFd.

[gibbz00]

• 1.65: pointer .cast_mut() (over as _)
• 1.75: pointer .byte_add() (over (ptr as *const u8).add(n) as *const T

[xtqqczze]

• 1.75: const_maybe_uninit_zeroed

[tgross35]

Bump to 1.65 in #4972