support fixedbinary(n) (#2348)

## Which issue does this PR close?

- Closes #2347 .

## What changes are included in this PR?

This change performs datum conversion for FixedSizedBinaryArray types
from fixed binary primitive types. It closely follows the previously
added support for Uuid types.

## Are these changes tested?

Yes

Author: jeff-sqds

crates/iceberg/src/arrow/schema.rs

@@ -762,6 +762,11 @@ pub(crate) fn get_arrow_datum(datum: &Datum) -> Result<Arc<dyn ArrowDatum + Send
             let array = FixedSizeBinaryArray::try_from_iter(vec![bytes].into_iter()).unwrap();
             Ok(Arc::new(Scalar::new(array)))
         }
+        (PrimitiveType::Fixed(_), PrimitiveLiteral::Binary(value)) => {
+            let array = FixedSizeBinaryArray::try_from_iter(std::iter::once(value.as_slice()))
+                .map_err(|e| Error::new(ErrorKind::DataInvalid, e.to_string()))?;
+            Ok(Arc::new(Scalar::new(array)))
+        }
 
         (primitive_type, _) => Err(Error::new(
             ErrorKind::FeatureUnsupported,
@@ -2154,6 +2159,18 @@ mod tests {
             assert!(is_scalar);
             assert_eq!(array.value(0), [66u8; 16]);
         }
+        {
+            let datum = Datum::fixed(vec![1u8, 2, 3, 4, 5, 6, 7, 8]);
+            let arrow_datum = get_arrow_datum(&datum).unwrap();
+            let (array, is_scalar) = arrow_datum.get();
+            let array = array
+                .as_any()
+                .downcast_ref::<FixedSizeBinaryArray>()
+                .unwrap();
+            assert!(is_scalar);
+            assert_eq!(array.value_length(), 8);
+            assert_eq!(array.value(0), &[1u8, 2, 3, 4, 5, 6, 7, 8]);
+        }
     }
 
     #[test]