Cleanup #[cfg(attr)] test annotations for wasm target

[insipx]

rel: rustwasm/wasm-bindgen#4139

Re-iterating issue above:

there should be a better way then repeating

    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test::wasm_bindgen_test)]
    #[cfg_attr(not(target_arch = "wasm32"), tokio::test(flavor = "multi_thread"))]

for every single test

maybe a proc macro that is target-aware? ie

#[test(tokio::test)]

where tokio:: is optional, but the attribute becomes [wasm_bindgen] or something