Fix a crash on ^C during a REPL command

[plotnick]

Interrupting a REPL command could crash the client with a core dump. The crash came from a stale rustyline signal handler writing to a closed pipe. Enabling rustyline's signal-hook feature makes it share the signal registry that tokio uses, and no stale handler remains installed.

Example crash:

sush# job start -i -T 14 bash
✅ Session is now `disorder-episode-young-unaware-will-token-page-sort`
⠐  Waiting for signature on `leopard-bar-force-hair-farm-volcano-fish-virus` [00:00:28]
^C
thread 'main' (1) panicked at /home/build/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rustyline-17.0.2/src/tty/unix.rs:83:18:
fd != -1
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread 'main' (1) panicked at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/core/src/panicking.rs:225:5:
panic in a function that cannot unwind
stack backtrace:
   0:          0x1a5e1c6 - <<std[a3c1d0ae1e0a836a]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[31c3886e4e16a981]::fmt::Display>::fmt
   1:          0x1a9ed1a - core[31c3886e4e16a981]::fmt::write
   2:          0x1a6e181 - <std[a3c1d0ae1e0a836a]::sys::stdio::unix::Stderr as std[a3c1d0ae1e0a836a]::io::Write>::write_fmt
   3:          0x1a340a4 - std[a3c1d0ae1e0a836a]::panicking::default_hook::{closure#0}
   4:          0x1a54a33 - std[a3c1d0ae1e0a836a]::panicking::default_hook
   5:          0x1a54d91 - std[a3c1d0ae1e0a836a]::panicking::panic_with_hook
   6:          0x1a34192 - std[a3c1d0ae1e0a836a]::panicking::panic_handler::{closure#0}
   7:          0x1a282f9 - std[a3c1d0ae1e0a836a]::sys::backtrace::__rust_end_short_backtrace::<std[a3c1d0ae1e0a836a]::panicking::panic_handler::{closure#0}, !>
   8:          0x1a3541c - __rustc[6ef78fba13ac776c]::rust_begin_unwind
   9:          0x1a9f4fc - core[31c3886e4e16a981]::panicking::panic_nounwind_fmt
  10:          0x1a9f43a - core[31c3886e4e16a981]::panicking::panic_nounwind
  11:          0x1a9f602 - core[31c3886e4e16a981]::panicking::panic_cannot_unwind
⠐  Waiting for signature on `leopard-bar-force-hair-farm-volcano-fish-virus` [00:00:28]                                            12:          0x1017a3c - rustyline[992a51073e1d6952]::tty::unix::sig_handler
  13:          0x1934f66 - signal_hook_registry[f8137fdb20e9e5c4]::handler
  14: 0xfffffc7fe9c3b916 - __sighndlr
Segmentation Fault (core dumped)