I noticed that the `llm.chat.*_tokens` attributes weren't in spans, and it turns out none of the attributes from the wrapped function make it in. only those added synchronously from within `wrapWithSpan` do.
A few things in play here:
1. Switch from `ZoneContextManager` (which doesn't work with native async/await) to `AsyncLocalStorageContextManager` (which does.)
2. (1) requires we use a pnpm patch, since wrangler requires that we import `async_hooks` statically, and the otel code `requires` it, and also requires that it's spelled `node:async_hooks`.
3. encode the payload we try to send _before_ doing the retry loop, so we don't re-encode for each attempt.
4. switch from `startActiveSpan` to `context.with` + `startSpan`. The latter allows us to wrap an async function. the former is for synchronous functions.
