fix: restore Exact precision for single-row-group NDV and round-trip write_row_group_number_distinct_values

Two CI fixes:
- parquet_writer.rs: read write_row_group_number_distinct_values back from
  WriterProperties in session_config_from_writer_props instead of using the default
- metadata.rs: restore Precision::Exact for single-row-group NDV so the
  aggregate_statistics optimizer can fold COUNT(DISTINCT) to constants

Author: Rich-T-kid

datafusion/common/src/file_options/parquet_writer.rs

@@ -633,8 +633,8 @@ mod tests {
                 schema_force_view_types: global_options_defaults.schema_force_view_types,
                 binary_as_string: global_options_defaults.binary_as_string,
                 skip_arrow_metadata: global_options_defaults.skip_arrow_metadata,
-                write_row_group_number_distinct_values: global_options_defaults
-                    .write_row_group_number_distinct_values,
+                write_row_group_number_distinct_values: props
+                    .write_row_group_number_distinct_values(),
                 coerce_int96: None,
                 coerce_int96_tz: None,
                 content_defined_chunking: props.content_defined_chunking().into(),

datafusion/datasource-parquet/src/metadata.rs

@@ -966,6 +966,9 @@ fn summarize_distinct_counts(
     }
 
     Ok(match max_distinct_count {
+        Some(distinct_count) if num_row_groups == 1 => {
+            Precision::Exact(distinct_count as usize)
+        }
         Some(distinct_count) => Precision::Inexact(distinct_count as usize),
         None => Precision::Absent,
     })