'signal-hook-async-std' uses old dependencies, leading to RUSTSEC-2024-0384 ('instant' is unmaintained)

We currently have an exception in maint/cargo_audit for RUSTSEC-2024-0384.

https://rustsec.org/advisories/RUSTSEC-2024-0384.html

[The instant crate] is no longer maintained, and the author recommends using the maintained web-time crate instead.

The only reason that 'instant' exists in arti is due to 'signal-hook-async-std', which depends on an old version of 'futures-lite'.

If we want to get rid of our RUSTSEC-2024-0384 exception, we either need to stop using 'signal-hook-async-std', or get some patches upstreamed so that 'signal-hook-async-std' uses a newer version of 'futures-lite'.