[FEAT] Automatically use Ray Runner if Ray is initialized

[jaychia]

1. Automatically switches Daft to use the Ray Runner if a user calls ray.init(...) before running any Daft querying
2. Also switches behavior to try and deprecate the DAFT_RAY_ADDRESS environment variable so that we can centralize on the normal RAY_ADDRESS behavior

This PR ensures the following behavior:

• If a user explicitly calls daft.context.set_runner_ray/py, this overrides all behavior
  • If a user calls daft.context.set_runner_ray with a specified address, but Ray is already initialized, we warn them that their address is being ignored
• Otherwise, on first execution Daft will attempt to retrieve the runner config from the current environment:
  • Check for the DAFT_RUNNER environment variable for RAY/PY
  • Check to see if Ray is initialized, and if we aren't running in a Ray worker: RAY
  • Fallback onto: PY

Ray connection detection, on driver vs on worker:

Warning if set_runner_ray is called with an address after Ray is already initialized:

[kevinzwang]

Had a few comments, but otherwise looks great!

A few more thoughts:

• The usage of the lock seems correct to me 👍
• Have you tested this manually, or maybe could we write some basic tests for this behavior?
• In set_runner_py, the docstrings say "this is the default behavior", that should be changed.

[codecov]

Codecov Report

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2282   +/-   ##
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  Coverage        ?   79.12%           
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  Files           ?      471           
  Lines           ?    54404           
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Files	Coverage Δ
daft/runners/ray_runner.py	90.35% <50.00%> (ø)
daft/context.py	76.29% <70.83%> (ø)

[kevinzwang]

LGTM 👍