Add built-in operator statistics providers

Adds a set of default StatisticsProvider implementations that cover the
most common physical operators:

- FilterStatisticsProvider: selectivity-based row count, reuses the same
  pre-enhanced child statistics, with post-filter NDV adjustment
- ProjectionStatisticsProvider: column mapping through projections
- PassthroughStatisticsProvider: passthrough for cardinality-preserving operators
  (Sort, Repartition, Window, etc.) via CardinalityEffect
- AggregateStatisticsProvider: NDV-product estimation for GROUP BY,
  delegates for Partial mode and multiple grouping sets (apache#20926)
- JoinStatisticsProvider: NDV-based join output estimation (hash, sort-merge,
  nested-loop, cross) with join-type-aware cardinality bounds and correct
  key-column NDV lookup
- LimitStatisticsProvider: caps output at the fetch limit (local and global)
- UnionStatisticsProvider: sums input row counts
- DefaultStatisticsProvider: fallback to partition_statistics(None)

Author: asolimando

datafusion/physical-plan/src/filter.rs

@@ -309,7 +309,7 @@ impl FilterExec {
     }
 
     /// Calculates `Statistics` for `FilterExec`, by applying selectivity (either default, or estimated) to input statistics.
-    fn statistics_helper(
+    pub(crate) fn statistics_helper(
         schema: &SchemaRef,
         input_stats: Statistics,
         predicate: &Arc<dyn PhysicalExpr>,

datafusion/physical-plan/src/lib.rs

@@ -80,14 +80,14 @@ pub mod joins;
 pub mod limit;
 pub mod memory;
 pub mod metrics;
+pub mod operator_statistics;
 pub mod placeholder_row;
 pub mod projection;
 pub mod recursive_query;
 pub mod repartition;
 pub mod sort_pushdown;
 pub mod sorts;
 pub mod spill;
-pub mod operator_statistics;
 pub mod stream;
 pub mod streaming;
 pub mod tree_node;