Data provider: add contexts cache to JSON-LD library

Use the "document loader" of the jsonld.js library on the frontend (like we already do on the backend) to avoid fetching the context on every compact/frame operation.

https://github.com/digitalbazaar/jsonld.js?tab=readme-ov-file#custom-document-loader

Find the existing backend document-loader implementation and the frontend data-provider entry point. Read the jsonld.js custom document loader documentation, then trace compact and frame operations to confirm where context requests occur. Done means the frontend reuses cached contexts instead of fetching them on every operation.

Written by the indexing model from the issue text.