Check if another process is already listening on the port before trying to spawn

[jleibs]

What

• Resolves: Irritating error on spawn with an instance already running #2551

Before we spawn, we now try connecting to the port to see if it's in use or not, allowing us to print a better error message and not waste time kicking off a subprocess that's just going to fail.

Before:

$ python docs/code-examples/point3d_random.py
Traceback (most recent call last):
  File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/jleibs/rerun/rerun_py/rerun_sdk/rerun/__main__.py", line 16, in <module>
    main()
  File "/home/jleibs/rerun/rerun_py/rerun_sdk/rerun/__main__.py", line 12, in main
    exit(bindings.main(sys.argv))
RuntimeError: Failed to bind TCP address "0.0.0.0:9876". Another Rerun instance is probably running. Address already in use (os error 98)

After:

$ python docs/code-examples/point3d_random.py
DEV ENVIRONMENT DETECTED! Re-importing rerun from: /home/jleibs/rerun/rerun_py/rerun_sdk
Found existing process on port 9876. Trying to connect.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested demo.rerun.io (if applicable)

• PR Build Summary
• Docs preview
• Examples preview
• Recent benchmark results
• Wasm size tracking