Check sqllogictests for any dangling config settings (#17914) (#20838)

## Which issue does this PR close?

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- Closes ##17914.

## Rationale for this change
In a previous PR #20474, I
added a bash script that parsed the `SLT` files and checked whether any
DataFusion configuration options were modified without being reset.

While that approach worked, it relied on external scripting and
additional parsing logic. This PR introduces a simpler and more direct
solution implemented in Rust.

At the end of each `SLT` test file execution, the current configuration
is compared with the default configuration using a `Drop`
implementation. If any configuration values were modified and not
restored, a warning is printed.

This approach is easier to maintain and keeps the validation logic
within the Rust codebase rather than relying on an external bash script.

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## What changes are included in this PR?
- Capture the default DataFusion configuration when the `SLT` runner is
initialized.
- Implement `Drop` for the DataFusion SLT engine.
- When an `SLT` file finishes executing, compare the current
configuration with the default configuration.
- If differences are detected, print a warning showing which
configuration options were modified.

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## Are these changes tested?
This behavior is exercised by the existing `SLT` test suite. The
configuration check runs automatically when each `SLT` file completes
execution.

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## Are there any user-facing changes?
No. This change only affects internal `SLT` test infrastructure and does
not modify any public APIs.

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---------

Co-authored-by: Martin Grigorov <martin-g@users.noreply.github.com>

Author: cj-zhukov

datafusion/sqllogictest/src/engines/datafusion_engine/runner.rs

@@ -15,6 +15,7 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use std::collections::HashMap;
 use std::sync::Arc;
 use std::{path::PathBuf, time::Duration};
 
@@ -38,29 +39,38 @@ pub struct DataFusion {
     relative_path: PathBuf,
     pb: ProgressBar,
     currently_executing_sql_tracker: CurrentlyExecutingSqlTracker,
+    default_config: HashMap<String, Option<String>>,
 }
 
 impl DataFusion {
     pub fn new(ctx: SessionContext, relative_path: PathBuf, pb: ProgressBar) -> Self {
+        let default_config = ctx
+            .state()
+            .config()
+            .options()
+            .entries()
+            .iter()
+            .map(|e| (e.key.clone(), e.value.clone()))
+            .collect();
+
         Self {
             ctx,
             relative_path,
             pb,
             currently_executing_sql_tracker: CurrentlyExecutingSqlTracker::default(),
+            default_config,
         }
     }
 
     /// Add a tracker that will track the currently executed SQL statement.
     ///
     /// This is useful for logging and debugging purposes.
     pub fn with_currently_executing_sql_tracker(
-        self,
+        mut self,
         currently_executing_sql_tracker: CurrentlyExecutingSqlTracker,
     ) -> Self {
-        Self {
-            currently_executing_sql_tracker,
-            ..self
-        }
+        self.currently_executing_sql_tracker = currently_executing_sql_tracker;
+        self
     }
 
     fn update_slow_count(&self) {
@@ -135,6 +145,49 @@ impl sqllogictest::AsyncDB for DataFusion {
     async fn shutdown(&mut self) {}
 }
 
+impl Drop for DataFusion {
+    fn drop(&mut self) {
+        let mut changed = false;
+
+        for e in self.ctx.state().config().options().entries() {
+            let default_entry = self.default_config.remove(&e.key);
+
+            if let Some(default_entry) = default_entry
+                && default_entry.as_ref() != e.value.as_ref()
+            {
+                if !changed {
+                    changed = true;
+                    self.pb.println(format!(
+                        "SLT file {} left modified configuration",
+                        self.relative_path.display()
+                    ));
+                }
+
+                let default = default_entry.as_deref().unwrap_or("NULL");
+                let current = e.value.as_deref().unwrap_or("NULL");
+
+                self.pb
+                    .println(format!("  {}: {} -> {}", e.key, default, current));
+            }
+        }
+
+        // Any remaining entries were present initially but removed during execution
+        for (key, value) in &self.default_config {
+            if !changed {
+                changed = true;
+                self.pb.println(format!(
+                    "SLT file {} left modified configuration",
+                    self.relative_path.display()
+                ));
+            }
+
+            let default = value.as_deref().unwrap_or("NULL");
+
+            self.pb.println(format!("  {key}: {default} -> NULL"));
+        }
+    }
+}
+
 async fn run_query(
     ctx: &SessionContext,
     is_spark_path: bool,