Adapt CUDA decimal tests to the storage bound

The GPU filter test stores its i256 case at a precision that admits i256,
and the Arrow export test for narrowing i256 storage below its precision
is removed since such storage can no longer be constructed.

Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>
Signed-off-by: Claude <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015zQPnFWRi7CWXHpgBE8CiF

Author: claude

vortex-cuda/src/arrow/canonical.rs

@@ -2254,21 +2254,6 @@ mod tests {
         .await
     }
 
-    #[crate::test]
-    async fn test_export_decimal_narrowing_errors() -> VortexResult<()> {
-        let mut ctx = CudaSession::create_execution_ctx(&crate::cuda_session())
-            .vortex_expect("failed to create execution context");
-        let array = DecimalArray::from_iter([i256::from_parts(0, 1)], DecimalDType::new(38, 0))
-            .into_array();
-
-        let err = array
-            .export_device_array_with_schema(&mut ctx)
-            .await
-            .unwrap_err();
-        assert!(err.to_string().contains("narrowing would require"));
-        Ok(())
-    }
-
     #[rstest]
     #[case::i64(
         DecimalArray::from_iter([i64::MIN, -1i64, 1, i64::MAX], DecimalDType::new(39, 0)).into_array(),

vortex-cuda/src/kernel/filter/decimal.rs

@@ -81,7 +81,7 @@ mod tests {
         Mask::from_iter([false, true, false, true, false])
     )]
     #[case::i256_values(
-        DecimalArray::from_iter([i256::from_i128(1), i256::from_i128(2), i256::from_i128(3), i256::from_i128(4), i256::from_i128(5)], DecimalDType::new(19, 5)),
+        DecimalArray::from_iter([i256::from_i128(1), i256::from_i128(2), i256::from_i128(3), i256::from_i128(4), i256::from_i128(5)], DecimalDType::new(39, 5)),
         Mask::from_iter([false, true, false, true, false])
     )]
     #[crate::test]