read after optimistic write & optimistic reactivity

[tantaman]

If a user strictly performs optimistic writes (without awaiting for the write to complete) they can issue a read that doesn't return what they expect.

The current design requires hitting the database to fulfill any query. So issuing a write that you don't await can result in a later query not returning the data in that write.

We can:

1. Update our query layer to understand if there are pending writes. If so, await them before returning the read.
   ^-- I think this might already be the case accidentally when using wa-sqlite-connector as all those operations are serialized

When we make changes for #46 we'll have to consider how it impacts this task.

Reactive queries do not update optimistically. This might not be a big deal but could lead to strange behavior where a component lags behind another. When tackling #49 we can address parts of this problem. E.g., by making single hop reactive queries resolve themselves in-memory.