Add VRF proof verification / generation to the Schnorrkel wrapper

[David-Petrov]

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[David-Petrov]

[KNOWN ISSUE] Build automation is broken. The original jar task for managing the native rust lib (removed by 015023e) was meant to pick up the lib as output from cargo (built for the current architecture) and place it in its corresponding place. This, however, is a single-target automation.
Our fork of PolkaJ requires multi-target builds, so this approach is not suitable, thus jar has been removed.
For now, manual intervention is necessary: paste the rust lib manually from ./polkaj-schnorrkel/build/rust/release (that's the cargo build result; path relative from repository root) into its corresponding target architecture folder under ./polkaj-schnorrkel/src/main/resources/native, before then building again to obtain the properly updated .jar.

Unfortunately, compilation for all target architectures must happen manually in a similar way as described above, before officially "deploying a new version" for multi-arch usage.

Is it worth investing effort into polishing the automation...?

[RESOLVED]: Discussed with @georg-getz, polishing the automation is not worth it for now, as priorities are different. This goes into TODO.md. For now, a detailed description of this necessary manual intervention is to be added to this fork's README.md.