Partially-Blind RSA verification not supported in browser

This library currently doesn't support PBRSA verification in browser due to `crypto.subtle` not allowing large public exponents, as mentioned in `README.md`.

I've created a small reproducible example here: https://github.com/karx1/blindrsa-repro that will illustrate the gap. Ideally, the browser page should show `valid? true`, but instead it shows `ERROR: OperationError`.

Start with the browser limitations described in README.md and run the linked blindrsa-repro example to observe the crypto.subtle OperationError. Trace the browser verification path in the library and determine what change is needed so the example reports valid? true without the error.

Written by the indexing model from the issue text.