wasm32-wasip2 target

[StuartHarris]

Everything compiles except the url crate, so I raised an issue. In the meantime, we're manually parsing the url for routing purposes, and importing form_urlencoded directly for query string parsing.

• bring crates into a single Cargo workspace
• no longer need cargo-component or wash to build components, rustc can do this itself
• wit-deps looks unmaintained to me, so have brought all wit deps in manually and referencing them explicitly when calling wit-bindgen::generate! macro
• set default target, so that cargo build works