Add support for Farcaster Frames

Frames are a new type of signed Farcaster Message. At the minimum, the sdk should have its type bindings extended to support returning Frame messages from the hub/neynar APIs. Ideally support is also added for creating and publishing Frame messages.

Details: https://warpcast.notion.site/Farcaster-Frames-4bd47fe97dc74a42a48d3a234636d8c5
