Fix FilterExec tree render missing fetch display

When `FilterExec` has a `fetch` (limit pushed down), the `TreeRender`
display format does not show it, while `Default`/`Verbose` formats do.
This makes `EXPLAIN FORMAT TREE` output incomplete for queries with
LIMIT pushed into FilterExec.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: zhuqi-lucas

datafusion/physical-plan/src/filter.rs

@@ -505,7 +505,11 @@ impl DisplayAs for FilterExec {
                 )
             }
             DisplayFormatType::TreeRender => {
-                write!(f, "predicate={}", fmt_sql(self.predicate.as_ref()))
+                write!(f, "predicate={}", fmt_sql(self.predicate.as_ref()))?;
+                if let Some(fetch) = self.fetch {
+                    write!(f, ", fetch={fetch}")?;
+                }
+                Ok(())
             }
         }
     }

datafusion/sqllogictest/test_files/limit.slt

@@ -385,6 +385,25 @@ SELECT COUNT(*) FROM (SELECT a FROM t1 WHERE a > 3 LIMIT 3 OFFSET 6);
 ----
 1
 
+# Verify that EXPLAIN FORMAT TREE shows fetch on FilterExec
+query TT
+EXPLAIN FORMAT TREE SELECT a FROM t1 WHERE a > 3 LIMIT 5;
+----
+physical_plan
+01)┌───────────────────────────┐
+02)│         FilterExec        │
+03)│    --------------------   │
+04)│         predicate:        │
+05)│       a > 3, fetch=5      │
+06)└─────────────┬─────────────┘
+07)┌─────────────┴─────────────┐
+08)│       DataSourceExec      │
+09)│    --------------------   │
+10)│         bytes: 160        │
+11)│       format: memory      │
+12)│          rows: 1          │
+13)└───────────────────────────┘
+
 # generate BIGINT data from 1 to 1000 in multiple partitions
 statement ok
 CREATE TABLE t1000 (i BIGINT) AS
@@ -867,7 +886,7 @@ limit 1000;
 
 # Config reset
 
-# The SLT runner sets `target_partitions` to 4 instead of using the default, so 
+# The SLT runner sets `target_partitions` to 4 instead of using the default, so
 # reset it explicitly.
 statement ok
 set datafusion.execution.target_partitions = 4;