DatabaseKit 2.0 (#53)

• remove all dependencies besides SwiftNIO; share connections across event loop

• add ThreadConnectionPool type and update pool algorithm

• add new test to manifest

• NIO 2 updates

• update to 4.2

• update to latest NIO 2 changes

• latest nio 2 updates

• cleanup extraneous files

• use connection pool from NIOKit

• update ci