Add argument for automatic TCP tunneling

[brentyi]

Here's a pass at automatically generating + printing a shareable link. It works for me — I can pass in share=True and it lets me connect to a nerfstudio viewer from a different machine/network.

The current implementation is similar to the nodeenv code that @origamiman72 wrote for client builds: it sets up a sandboxed Rust environment and builds + runs bore. bore seemed like the simplest of many options, some of which are surveyed here: https://github.com/anderspitman/awesome-tunneling

Some notes:

• TCP forwarding was pretty straightforward manually. Maybe we could just leave this out of the codebase, and point folks to resources for this.
• We do some manual parsing of bore log messages currently, which seems brittle.

[brentyi]

Obsolete!