feat(csharp): Be more rigorous about "state hygiene"

For instance, consider not allowing a connection to be closed while there's still a reader active. For the ADO.NET wrapper, don't allow the driver or other properties to be changed while the connection is open. For consistency with other ADO.NET providers, consider not auto-opening the connection when a command is created. Be precise about the number of open statements/commands that can be associated with a connection.