feat: Add new() constructor for CachedParquetFileReader (apache#18575)

## Which issue does this PR close?

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- Closes apache#18145

## Rationale for this change

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Allows constructing `CachedParquetFileReader::new()` manually, allowing
users to create it with a custom object reader (inner) object.

## What changes are included in this PR?

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PR.
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Adds a simple constructor for `CachedParquetFileReader`

## Are these changes tested?

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Added a test

## Are there any user-facing changes?

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Yes, new constructor available

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Author: petern48

datafusion/datasource-parquet/src/reader.rs

@@ -208,14 +208,14 @@ impl ParquetFileReaderFactory for CachedParquetFileReaderFactory {
             inner = inner.with_footer_size_hint(hint)
         };
 
-        Ok(Box::new(CachedParquetFileReader {
-            store: Arc::clone(&self.store),
-            inner,
+        Ok(Box::new(CachedParquetFileReader::new(
             file_metrics,
+            Arc::clone(&self.store),
+            inner,
             partitioned_file,
-            metadata_cache: Arc::clone(&self.metadata_cache),
+            Arc::clone(&self.metadata_cache),
             metadata_size_hint,
-        }))
+        )))
     }
 }
 
@@ -231,6 +231,26 @@ pub struct CachedParquetFileReader {
     metadata_size_hint: Option<usize>,
 }
 
+impl CachedParquetFileReader {
+    pub fn new(
+        file_metrics: ParquetFileMetrics,
+        store: Arc<dyn ObjectStore>,
+        inner: ParquetObjectReader,
+        partitioned_file: PartitionedFile,
+        metadata_cache: Arc<dyn FileMetadataCache>,
+        metadata_size_hint: Option<usize>,
+    ) -> Self {
+        Self {
+            file_metrics,
+            store,
+            inner,
+            partitioned_file,
+            metadata_cache,
+            metadata_size_hint,
+        }
+    }
+}
+
 impl AsyncFileReader for CachedParquetFileReader {
     fn get_bytes(
         &mut self,