[FEAT] Implement splitting of Project into actor pool projects

Implement core logic

Add TreeNodeRewriter logic

Add passing unit test

Add test with multiple stateful projections

Add another test that is currently failing

src/daft-dsl/src/expr.rs

@@ -612,7 +612,7 @@ impl Expr {
         }
     }
 
-    pub(super) fn with_new_children(&self, children: Vec<ExprRef>) -> Expr {
+    pub fn with_new_children(&self, children: Vec<ExprRef>) -> Expr {
         use Expr::*;
         match self {
             // no children

src/daft-plan/src/logical_optimization/rules/mod.rs

@@ -3,6 +3,7 @@ mod push_down_filter;
 mod push_down_limit;
 mod push_down_projection;
 mod rule;
+mod split_actor_pool_projects;
 
 pub use drop_repartition::DropRepartition;
 pub use push_down_filter::PushDownFilter;