Golang: Make each 'Client' have an independent 'ClientManager'

Currently a process globally shares a 'ClientManager', so only one 'Conn' is established for each endpoint. When users create a new client, their expectations should be completely independent.


Read the Golang Client and ClientManager implementation first, tracing where the process-wide manager and endpoint connections are created. Verify how multiple clients currently share a Conn, then make independence observable by ensuring each Client can establish and manage its own connection for the same endpoint.

Written by the indexing model from the issue text.