[FEAT] Introduce actor pool physical plan

[jaychia]

TODOs:

General

• [ ] Properly propagate the num_actors to the physical plan from some user-facing API (TBD)
• [ ] Fix the translation logic to correctly account for arbitrarily nested stateful/stateless UDFs across the entire projection list. Also when running simple projections like a + 1, or .alias(), should we just do it on the actor?
• [x] Extend the ActorPoolProject physical node to also be a Logical concept
• [x] Explore creating a new type of PartitionTask which is a PythonUDFPartitionTask. The current PartitionTask doesn't work great for expressing the physical plan because we just tag on single "marker" no-op instruction that isn't actually useful for execution.
• [ ] Ensure proper teardown of actor pools (especially when faced with failures)

Ray

• [x] Properly name the actor pools for Ray debuggability
• [ ] Fix and figure out how to make this code work for remote Ray clusters, because the resource accounting and ray actor pools are being held remotely in the SchedulerActor, but the physical plan is run (I think?) locally? I might be wrong here.
• [ ] Properly initialize the execution config per-actor based on the current run ID, instead of naively taking it from the environment

Py

• [ ] Properly reserve resources for PyRunner's actor pools

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 31.74603% with 172 lines in your changes missing coverage. Please review.

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Additional details and impacted files

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Files	Coverage Δ
daft/execution/execution_step.py	94.20% <100.00%> (ø)
daft/udf.py	92.96% <100.00%> (ø)
src/daft-dsl/src/functions/python/mod.rs	100.00% <100.00%> (ø)
src/daft-dsl/src/python.rs	93.21% <100.00%> (ø)
daft/expressions/expressions.py	93.68% <66.66%> (ø)
daft/execution/rust_physical_plan_shim.py	94.38% <33.33%> (ø)
daft/runners/runner.py	82.85% <72.72%> (ø)
src/daft-plan/src/physical_plan.rs	49.43% <28.57%> (ø)
src/daft-execution/src/stage/planner.rs	0.00% <0.00%> (ø)
src/daft-plan/src/physical_planner/translate.rs	92.15% <78.37%> (ø)
... and 5 more