Add Observe SDK support to the Extism runtime

[bhelx]

It would be great if we had Observe support in the Extism runtime. For ourselves and for our users. I think the primary blocker on this one is tokio / async support in Extism as that's required by the SDK. Perhaps there is another way.

@zshipko do you mind filling in some details on what we need to accomplish this goal?

[zshipko]

I have tried converting the runtime to use the wasmtime async API, but this complicates the C API because we need to block on the future to return it from the SDK functions. It brings up the question of what runtime to support, do we go with tokio or try to support async-std too? I think doing this would still be possible but it's a lot of work.

The thing I haven't tried is to re-implement the observe SDK as Extism host functions in https://github.com/extism/extism/blob/main/runtime/src/pdk.rs - which seems like the most realistic path to observe support with what is available in Extism today.

[neuronicnobody]

Only Otel support

[neuronicnobody]

@bhelx follow up with Zach on priority for this