feat: Incorporate wasi-clocks changes

[cdmurph32]

Recent changes to wasi-clocks have replaced wall-clock with system-clock
WebAssembly/wasi-clocks#79
The record instant replaces datetime. Seconds are now signed.

    record instant {
        seconds: s64,
        nanoseconds: u32,
    }

replaces

    record datetime {
        seconds: u64,
        nanoseconds: u32,
    }

[yoshuawuyts]

What we might actually do here is rev a new 0.3 RC, and then you can go directly from there. Let me ping some people before doing that to make sure that won't cause any problems.

[yoshuawuyts]

Oh I see, yeah no we can't just rev a clocks release. We have to merge this on main, and then bump all the versions in lockstep afterwards. If we don't do that we'll risk publishing a broken release. So from a process perspective this PR looks good to me!