Fetch the app's primary feed call (POST, protobuf) decoded without a schema

Calls the app's primary feed route - POST /aweme/v2/feed/, which the Android client sends with a protobuf request body and answers with protobuf - and returns a schema-free decode: field numbers become keys, length-delimited fields become strings when printable, nested messages when they parse and base64 otherwise, plus a flat list of every string leaf. Field numbering is inferred because TikTok publishes no schema for this message; use the JSON GET /tiktok/mobile/feed route when you need the stable structured contract.