add $type key to blob and lexicon ref fields in graphql mutations
Automatically adds $type key when transforming GraphQL data to AT Protocol
format in mutations:
- Blob fields: adds "$type": "blob"
- Lexicon refs: adds "$type": "{ref_nsid}" (e.g., "community.lexicon.location.hthree#main")
- Handles single values, arrays, and nested objects recursively
Renamed transform_blob_fields_for_atproto to transform_fields_for_atproto
to reflect expanded functionality.