Generalize null-rejection checks into a reusable expression trait

[SubhamSinghal]

Is your feature request related to a problem or challenge?

Discussion thread

Several optimizer rules need to determine whether an expression "rejects nulls" — i.e., returns NULL/false when one or more input columns are NULL. Today this logic lives in EliminateOuterJoin's extract_non_nullable_columns() with explicit pattern matching for each expression type (comparison, IN, BETWEEN, LIKE, IS TRUE/FALSE, etc.). Every new expression type must be added manually.

Describe the solution you'd like

Introduce a NullRejection trait on expressions, similar to Apache Calcite's Strong class:

 trait PhysicalExpr {
     // ... existing methods ...

     /// Returns whether this expression is guaranteed to be not-true
     /// (i.e., NULL or false) when all given columns are NULL.
     ///
     /// - `Some(true)`:  definitely rejects nulls (safe to eliminate outer join)
     /// - `Some(false)`: definitely does NOT reject nulls
     /// - `None`:        unknown (conservative default, assume not null-rejecting)
     fn is_not_true(&self, all_null_cols: &[&Column]) -> Option<bool> {
         None
     }
 }

Each expression type overrides with simple structural logic:

// Comparison (=, >, <, etc.): NULL on either side → NULL result
impl PhysicalExpr for BinaryExpr {
    fn is_not_true(&self, all_null_cols: &[&Column]) -> Option<bool> {
        match (self.left.is_not_true(all_null_cols), self.right.is_not_true(all_null_cols)) {
            (Some(true), _) | (_, Some(true)) => Some(true),
            (Some(false), Some(false)) => Some(false),
            _ => None,
        }
    }
}

Describe alternatives you've considered

No response

Additional context

No response

[SubhamSinghal]

take