fix(fullstack): don't panic on incomplete request bodies

[cestercian]

Summary

Incomplete client bodies can fail Bytes::from_request in production. The one-arg ExtractRequest path was unwrapping that error, which panics the server (FailedToBufferBody).

Change

Bubble the rejection the same way header extraction already does:

let bytes = Bytes::from_request(request, &())
    .await
    .map_err(|e| e.into_response())?;

No anyhow. Sibling extractors (msgpack / cbor / postcard) already used ?.

Test

Unit test drives extract_axum with an erroring body and asserts 400 Bad Request instead of a panic.

cargo test -p dioxus-fullstack --lib
cargo test -p dioxus-fullstack --features server --lib
cargo clippy -p dioxus-fullstack --lib --tests --all-features -- -D warnings

Fixes #5018