Proposed namespace: Wallet

[bumblefudge]

Rather than hardcode a special-case into CAIP-25, I would propose hard-coding an "abstraction" namespace for the special-case of subsetting other namespaces (for the purposes of, say, enabling an app<>wallet connection or app<>wallet RPC methods from a given L1 without needing to request and receive a network connection for that L1).

@Vandan @jiexi @gudahtt for discussion next week-- feel free to commit or PR against the branch if you have ideas, changes, examples for the "## Test Cases" section, and/or considerations about privacy, security, transport diversity, etc. Maybe this is a helpful starting point for other conversations around post-provider-injection transports?

Proposed as an alternative approach to CAIPs#303

also closes #55 if merged.