docs: pass access_plan directly in with_extension example

`with_extension<T>` keys by the concrete type `T`, so wrapping the
plan in `Arc::new(...)` would store it as `Arc<ParquetAccessPlan>`.
The downstream lookup is `extensions.get::<ParquetAccessPlan>()`,
which would miss the wrapped value and scan all row groups.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: adriangb

datafusion/datasource-parquet/src/source.rs

@@ -230,7 +230,7 @@ use parquet::encryption::decrypt::FileDecryptionProperties;
 /// access_plan.skip(4);
 /// // provide the plan as extension to the FileScanConfig
 /// let partitioned_file = PartitionedFile::new("my_file.parquet", 1234)
-///   .with_extension(Arc::new(access_plan));
+///   .with_extension(access_plan);
 /// // create a FileScanConfig to scan this file
 /// let config = FileScanConfigBuilder::new(ObjectStoreUrl::local_filesystem(), Arc::new(ParquetSource::new(schema())))
 ///     .with_file(partitioned_file).build();