fix(retrieval): store the BM25 index as gzipped JSON instead of pickle (#13)

fix(retrieval): budget skip, standard RRF, fail-fast collection load

Enhance knowledge base and API functionality

Renamed 'scripts' folder to 'app', removed mongo and instructor libraries

Refactor test cases for improved clarity and functionality

ruff format

Refactor scraping scripts to enhance source management and contextual node processing. Introduce new helper functions for pruning inactive contextual nodes and managing llms.txt sources. Update existing scripts to utilize the new source registry for improved source handling and streamline the process of adding and updating courses. Enhance error handling and logging for better traceability during data processing.