[FEAT] (ACTORS-1) Add DAFT_ENABLE_ACTOR_POOL_PROJECTS=1 feature flag and specifying concurrency

[jaychia]

1. Creates a new planning-time feature flag DAFT_ENABLE_ACTOR_POOL_PROJECTS=1 which controls whether or not we're using our actor-based stateful projections
2. Adds a new .with_concurrency(...) API for stateful UDFs that will allow users to configure the concurrency of each UDF before calling it. Note that if DAFT_ENABLE_ACTOR_POOL_PROJECTS=1 is enabled then the users will have to call this, otherwise the UDF will fail to run with a ValueError.
3. Modifies logic across our ActorPoolProject to derive its concurrency factor (previously called num_actors) from its projection instead.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 58 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@291bd96). Learn more about missing BASE report.
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Files	Patch %	Lines
...c/daft-plan/src/physical_ops/actor_pool_project.rs	0.00%	22 Missing ⚠️
src/daft-dsl/src/functions/python/mod.rs	9.09%	20 Missing ⚠️
daft/udf.py	55.55%	4 Missing ⚠️
...rc/daft-plan/src/logical_ops/actor_pool_project.rs	20.00%	4 Missing ⚠️
src/common/daft-config/src/lib.rs	72.72%	3 Missing ⚠️
src/daft-plan/src/logical_plan.rs	0.00%	1 Missing ⚠️
...sical_optimization/rules/reorder_partition_keys.rs	0.00%	1 Missing ⚠️
src/daft-plan/src/physical_plan.rs	0.00%	1 Missing ⚠️
src/daft-plan/src/physical_planner/translate.rs	0.00%	1 Missing ⚠️
src/daft-scheduler/src/scheduler.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2668   +/-   ##
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  Coverage        ?   63.73%           
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  Files           ?      979           
  Lines           ?   111588           
  Branches        ?        0           
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  Hits            ?    71121           
  Misses          ?    40467           
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Files	Coverage Δ
daft/context.py	76.59% <100.00%> (ø)
daft/expressions/expressions.py	93.71% <ø> (ø)
src/common/daft-config/src/python.rs	67.32% <100.00%> (ø)
src/daft-dsl/src/python.rs	94.10% <100.00%> (ø)
...logical_optimization/rules/push_down_projection.rs	84.02% <100.00%> (ø)
src/daft-plan/src/logical_plan.rs	72.83% <0.00%> (ø)
...sical_optimization/rules/reorder_partition_keys.rs	80.21% <0.00%> (ø)
src/daft-plan/src/physical_plan.rs	54.24% <0.00%> (ø)
src/daft-plan/src/physical_planner/translate.rs	91.67% <0.00%> (ø)
src/daft-scheduler/src/scheduler.rs	89.10% <0.00%> (ø)
... and 5 more

[desmondcheongzx]

LGTM