Parallel execution in rln-wasm

[richard-ramos]

Currently multithreading support in rln-wasm is disabled by not using the parallel feature, due to the following error:

The global thread pool has not been initialized.: ThreadPoolBuildError { kind: IOError(Error { kind: Unsupported, message: "operation not supported on this platform"

Some changes in code might be required to support multithreading in the browser. Here are some resources to explore:

• https://rustwasm.github.io/wasm-bindgen/examples/wasm-in-web-worker.html
• https://github.com/GoogleChromeLabs/wasm-bindgen-rayon

Something to take in account that any changes done here must be tested in https://github.com/waku-org/js-rln