feat: Automatically assign ports when available

[ShrimpCryptid]

Problem

Change by @alexkhang18 that I'm PRing on his behalf, with a few minor changes. This change allows the tfe-open command to automatically assign new port numbers if the current ones are occupied.

Estimated review size: tiny, 5 minutes

Testing

1. Initialize a virtual environment if needed.
2. Run pip install -e '.[dev]'
3. Run tfe-open documentation/example_dataset. A new browser window should open.
4. Repeat the above steps in another window.

Video talk-through (🔊):

2025-10-13.15-57-42.mp4

[rugeli]

it's a handy feature! left a non-blocking note

[rugeli]

smart choice making it recursive! There is a recursion depth limitation with python but we're unlikely to hit it with just few ports so it's totally fine.
Although another thought I have, return a list of tuples like [(socket, port), ...] instead of just port numbers, then s.close() to close the sockets only after the servers running(or on error). This way should be safer because the ports stay reserved until we successfully started the servers on them

[ShrimpCryptid]

This is a good idea, thank you, Ruge!

[rugeli]

Looks great!