Hide cast module and update internal access

Make the cast module private again by changing its
visibility to module only. Provide crate-internal access
to the helper function from expressions::mod, and update
the planner to use this internal entry point instead
of direct module exposure.

Author: kosiew

datafusion/physical-expr/src/expressions/mod.rs

@@ -20,7 +20,7 @@
 #[macro_use]
 mod binary;
 mod case;
-pub(crate) mod cast;
+mod cast;
 mod cast_column;
 mod column;
 mod dynamic_filters;
@@ -41,6 +41,7 @@ pub use crate::aggregate::stats::StatsType;
 
 pub use binary::{BinaryExpr, binary, similar_to};
 pub use case::{CaseExpr, case};
+pub(crate) use cast::cast_with_target_field_and_options;
 pub use cast::{CastExpr, cast};
 pub use cast_column::CastColumnExpr;
 pub use column::{Column, col, with_new_schema};

datafusion/physical-expr/src/planner.rs

@@ -289,7 +289,7 @@ pub fn create_physical_expr(
             Ok(expressions::case(expr, when_then_expr, else_expr)?)
         }
         Expr::Cast(Cast { expr, field }) => {
-            expressions::cast::cast_with_target_field_and_options(
+            expressions::cast_with_target_field_and_options(
                 create_physical_expr(expr, input_dfschema, execution_props)?,
                 input_schema,
                 Arc::clone(field),