C#: Add port autodetection and make `port` parameter optional

[mindsolve]

Feature Description

We should have feature parity between different MineStat editions. The Python (and other) editions made the port parameter optional, if it can be automatically detected, e.g. through SRV records or default ports.

• Add port autodetection for default ports
• Make port parameter optional
• Document new usage patterns in README and docstring

Originally proposed by @nimeng1299 in issue #237