Add Support for TCP Mode

[oneingan]

It would be great to have support for TCP mode in TSDProxy to handle raw TCP traffic in addition to HTTP. This would allow for more versatile use cases, such as proxying non-HTTP protocols within Tailscale networks.

Use Case:
For example, proxying database connections or other custom TCP-based services through TSDProxy.

Request:
Please consider adding a TCP mode feature to expand TSDProxy's capabilities.

Thank you for your consideration!