Refactor RSA verification: Replace jsrsasign with crypto-js

[lbalmaceda]

Changes

jsrsasign library was not compatible with the Hermes JS engine, currently optional but still officially supported by the React Native platform for Android. This PR changes the RSA signature check implementation to use crypto-js instead.

No breaking changes are introduced on this build.

References

Resolves #251

Testing

The unit tests were updated. To evaluate Hermes support, it has been tested this way:

1. Enable Hermes for your android app by changing the app/build.gradle file

 project.ext.react = [
     entryFile: "index.js",
     enableHermes: true,  // clean and rebuild if changing
 ]

2. Clean and Rebuild

cd android && ./gradlew clean assemble

3. Run the android app in a "release" variant

react-native run-android --variant release

• This change adds unit test coverage
• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines
• All existing and new tests complete without errors
• All active GitHub checks have passed

[Widcket]

I suggest you reword this to use present simple describing what it should do, instead of simply repeating the function name.

[lbalmaceda]

I don't see other choices here. The method's responsibility is pretty dumb, TBH. Only decoding a base64 into a HEX value. What do you have in mind?

[Widcket]

LGTM