More rust tests for update commitment JNI function

[dragan2234]

Make more tests for the work done here: #10
This has only trivial tests using Fr::0 and Fr::1, it would be good to have more complicated and real-world values tests.

For example:

1. Commit to 256 values(field elements).
2. Update i-th value
3. Commit to 256 values where i-th value is already changed.

Compare if 2nd result is equal to 3rd.

[MatteoMer]

It would also be good to have theses tests (existing+the one in the issue) written as java tests (not only rust), calling the JNI rust lib!