Fix lifespan execution order

[jordaneremieff]

While working on the example app I've run into an issue when interacting with the database in post requests. The initial request seems to work fine (db on startup/on close execute properly in lifespan context), but if I make a post request using a form (e.g. a login) the connection pool isn't acquired. I think this is because the lifespan startup should be run not in the adapter constructor, but rather in the event handler - this seemed to work and makes sense.

I'll make a PR for this change.