feat(0.3): rework stream error handling/remove wasi:io usage

[rvolosatovs]

Remove wasi:io usage in wit-0.3.0-draft

Followed the same stream error handling convention as currently in

• feat: add wasi-0.3.0 draft wasi-filesystem#164
• feat: add wasi-0.3.0 draft wasi-sockets#111

[lukewagner]

The change to the constructor/new is actually pretty interesting, because it demonstrates how the "return a future<result<_, error-code>>" trick is necessary not just for functions returning a stream, but also functions taking a stream, and thus even the stream<T,SuccessT,ErrorT> extension (presented here) wouldn't eliminate it. This raises some interesting questions on whether the ErrorT should be able to flow both ways... but that's all for later, and I think what you're doing here is about the only possible thing we can do in a 0.3.0 timeframe to not regress from 0.2, which provided error-codes upon write failures. Nice work! (cc @dicej )

[rvolosatovs]

@lukewagner I've rebased on latest main to pull in the change from #142 and resolve a merge conflict

[lukewagner]

Given all the things in flight, I wasn't sure when's a good point to merge (and iterate in later PRs), but seems fine to merge now?

[rvolosatovs]

Given all the things in flight, I wasn't sure when's a good point to merge (and iterate in later PRs), but seems fine to merge now?

I think it's fine to merge now indeed