format: also define DatabaseCancel

[lidavidm]

What feature or improvement would you like to see?

Necessary if you want to cancel opening a connection (not much else needs it)

[CurtHagenlocher]

It might also be worth adding an AdbcConnectionInitAsync to the async proposal.

[lidavidm]

Hmm, looking at the specific case of cancelling opening a new connection, arguably the solution could be to make implementations of ConnectionCancel work between New and Init? Since the act of connection is actually AdbcConnectionInit.

CC @amoeba - I noticed CtrlC doesn't work when connecting, looking at it I think we "just" need to adjust the Go FFI shims and Python driver manager to cooperate.