rustix 1.1.5 breaks the Linux attach build: rustix::runtime is no longer public #230

Summary

rmux-client 0.10.0 fails to build on Linux against rustix 1.1.5. rustix 1.1.5 renamed the
runtime module to a mangled, private name (rustix::runtime_448b8ad740e2a26f) and re-exports it
only as pub(crate) (bytecodealliance/rustix#1633), so a downstream use rustix::runtime::… no
longer resolves.

src/attach/resize/linux.rs imports the module directly:

use rustix::runtime::{kernel_sigprocmask, kernel_sigwait, tkill, How, KernelSigSet};

Reproduction

[dependencies]
rustix = "1.1.5"

$ cargo check --target x86_64-unknown-linux-gnu
error[E0432]: unresolved import `rustix::runtime`
 --> src/attach/resize/linux.rs:8:18
  |
8 | use rustix::runtime::{kernel_sigprocmask, kernel_sigwait, tkill, How, KernelSigSet};
  |                  ^^^^^^^ could not find `runtime` in `rustix`

rustix 1.1.4 builds (its runtime module was public). macOS is unaffected because the file is
#[cfg(target_os = "linux")]-only.

Fix

Either pin rustix = "=1.1.4", or move the Linux signal handling off the now-private
rustix::runtime API (e.g. nix / libc), so the crate builds against current rustix.