Extend base test suite with p50k_base and r50k_base token examples

See:
* https://github.com/knuddelsgmbh/jtokkit/blob/main/lib/src/test/resources/p50k_base_encodings.csv
* https://github.com/knuddelsgmbh/jtokkit/blob/main/lib/src/test/resources/r50k_base_encodings.csv

Author: Lőrinc