0.3.2-beta3

Add back some helpers used by xmtp-rust-swift, expose via ffi (#229)

0.3.2-beta0

Simplify external API interface (#206)

1. Make all methods of `Conversations` static, and accept a `Client` argument, so that `Conversations` doesn't need to be instantiated anywhere. `Conversations` doesn't really hold state anyway and effectively functions as a wrapper for `Client` right now, so it doesn't make sense for consumers to have to instantiate it and hold onto it.
2. Call `process_outbound_messages()` on init and on message send, so that consumers don't have to manually call it.
3. Limit the connection pool size to 1 for the ephemeral DB instance, because when multiple connections are made, each one operates on a separate database. In the event that a connection is requested from the pool while another one is ongoing, it will wait for a time limit before expiring with an error. An added plus of this is it's much easier for tests to detect deadlocks.

This simplifies the client API quite a bit, as can be seen in `bindings_ffi` and in the `CLI`.

Ideally, we could have spawned a separate thread to call `process_outbound_messages` so that the existing thread is not blocked, but that requires additional refactoring. This requires us to enforce `XmtpApiClient` is `Send + Sync` (which is easy), but also comes up against issues with lifetimes for `Client`, for which a reference is needed in the other thread that may outlive the current thread. This possibly requires us to start using `Arcs` again.