Update SDK to support WASIP2

[kate-goldenring]

This work was started by @rajatjindal and @adamreese on this branch but could use help picking it up https://github.com/spinframework/spin-go-sdk/tree/wasip2

SDKs to update:

• HTTP (the branch has already completed this)
• KV feat(wasip2/kv): add support for wasip2 kv #17
• LLM add llm support for wasip2 sdk #18
• Variables Add support for wasip2 variables #19

[rajatjindal]

I have wip branches that implement some of these, i will find them and open up next pr

[adamreese]

Converting remaining SDK's to sub-issues