Spin 4.0

[itowlson]

Work in progress! I've put the initial "fork all the things" stuff in the initial commit so in principle you can review the boilerplate for boilerplatey things and the content changes for actual content separately, but I dunno, maybe I should make two separate PRs, anyway, v4, WIP.

File	Changes	Status (I think)
api-guides-overview.md	Noted asyncness - need to confirm which APIs we are asyncifying
build.md	Build profiles - added	Completed
cache.md	None	Completed
cli-reference.md	Regenerate when Spin 4 stabilises	Pending v4 readiness
contributing-docs.md	None	Completed
contributing-spin.md	None	Completed
deploying.md	Remove Fermyon Cloud	Completed
distributing-apps.md	Build profiles - added	Completed
dynamic-configuration.md	None	Completed
extending-and-embedding.md	None	Completed
go-components.md
http-outbound.md	http_service-fied Rust. Streaming outbound reqs/resps in Rust - done (check once SDK lands). TODO: Go, JS, Python.	Started
http-trigger.md	Instance reuse - added. http_service - added.	Started
index.md	None	Completed
install.md	None	Completed
javascript-components.md	TBA
kv-store-api-guide.md	Asyncified Rust. TODO: JS, Python, Go	Started
language-support-overview.md
managing-plugins.md	None	Completed
managing-templates.md	None	Completed
manifest-reference.md	Build profiles - added	Completed
mqtt-outbound.md	Asyncified Rust. TODO: JS, Python, Go	Started
observing-apps.md	None I think (wasi-http isn't asyncified yet)	Completed
other-languages.md
plugin-authoring.md	None	Completed
python-components.md	TBA
quickstart.md	Removed Fermyon Cloud stuff (do we want to talk more about deploying here? I added a link to the deployment options page). Asyncified Rust. TODO: JS, Python, Go.	Started
rdbms-storage.md	PG only is now async/streaming	Completed
redis-outbound.md	Asyncified Rust. TODO: JS, Python, Go	Started
redis-trigger.md	Async entry point, renamed Rust attribute. TODO: Python, Go SDKs (JS doesn't do Redis)	Started
running-apps.md	Nothing to do here?	Completed
rust-components.md	Asyncified, derouterised, de-http-crated. Need to verify that the SDK accepts borrows but basically	Completed
see-what-people-have-built-with-spin.md	None	Completed
serverless-ai-api-guide.md	Asyncify HTTP context stuff, no change to LLM API. Done for Rust. TODO: JS, Python, Go	Started
spin-application-structure.md	Changed http_component to http_service. Revisit once template and response body stuff is sorted.
sqlite-api-guide.md
template-authoring.md	None	Completed
testing-apps.md	We believe this doesn't work with P3. Removing for now	Done
triggers.md	I don't think there are any changes here	Completed
troubleshooting-application-dev.md	Remove spin test reference until we can work on that	Done
upgrade.md	None	Completed
variables.md	Async, http_service, response guff	Started
writing-apps.md	Just some asyncifying I think	Completed

General things:

• Updated remaining wasm32-wasip1 to wasm32-wasip2