feat: RPC cleanup, high level API declarations

[harrysolovay]

This PR is getting a bit massive, hence the rename. What does it contain?:

• A cleaned up Beacon type, which will serve as the basis for chain discovery / will encapsulate all chain/node-specific types
• Create known dir, containing known beacon/chain instances and move std RPC method lookup into this dir / decouple from RPC client
• Make RPC client (method signatures) generic over beacon
• Local RPC client, which runs and connects to executable
• Update sr25519 bindings to suit test accounts
• Model high-level API
• Rough implementation of read-specific capabilities of high-level API
• (temporarily?) remove effect-based API
• Clean up examples