Refactor Bot Storage

[bertybuttface]

We are currently using Keyv as that just so happens to be what the waylaidwanderer package is using. It supports files, sqlite and other flavours of SQL but we use our own storage wrapper and it is poorly tested. We also don't have great context.

Matrix-bot-sdk have switched their storage backend to a choice of sqlite or postgresql without any 3rd party packages like Keyv. We should switch to using this natively.

We will then likely be dropping support for waylaidwanderer so we can get some actual decent AI conversation context storage too.