Segfault when closing while async operations are happening

For instance, this will segfault because the AsyncBucket is connecting in the background...

auth = PasswordAuthenticator(username="Administrator", password="password")

c = Cluster("couchbase://localhost", ClusterOptions(authenticator=auth))

await c.on_connect()

b = c.bucket("default")

# uncomment this, and no crash

# await b.on_connect()

await c.close()

Of course, we can't prevent all racing, but lets think about how to make this better. First off, lets insure close() is being called when a Cluster is deleted, so users never need to call it.

At that point, we can figure out if we want something which helps with this, since it is a misuse of the api, but not an obvious one. Some options:

• c.bucket(...) could return an Awaitable, which makes this scenario not possible
• we could think about holding weak references to the conn object in places we use it (bucket, collection, etc...). There's still a race here though, I believe...
• we could find a way to chain the close off any existing operations (but that sounds difficult/complex, however maybe not?)
• Something else.

This ticket needs to address the close() not being necessary to call - that seems like the first level of defense. We can spawn a new ticket for any ancillary work (perhaps for later), when we decide we need it.