Improve fullstack build performance via parallelization

[ochrons]

Feature Request

When building a fullstack project where the server takes longer to build than the WASM client, Dioxus waits until both builds complete before doing the wasm-bindgen phase. This, however, wastes time as wasm-bindgen could be done in parallel while the server is still building.

For example on my code space a small change in shared code causes a rebuild where wasm side takes 1.9sec while the server takes 6.5sec. Wasm-bindgen takes an additional 4.0sec, with total build time coming to 10.5sec.

Implement Suggestion

If wasm-bindgen was ran directly after wasm build, in parallel with ongoing server build, the whole build time could potentially shrink to under 7 seconds.