feat(facade): Dataset::raw_datatype returns the full stored datatype

dtype() simplifies the type (no byte order, string padding or member
offsets), so callers could not decode read_selection's bytes for types
the typed read_* methods skip. raw_datatype() returns the parsed
Datatype, committed types resolved, for use with data_read.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5/src/lib.rs

@@ -144,6 +144,35 @@ mod tests {
         assert_eq!(ds.dtype().unwrap(), DType::I32);
     }
 
+    #[test]
+    fn dataset_raw_datatype() {
+        use clawhdf5_format::datatype::Datatype;
+        let bytes = make_simple_file();
+        let file = File::from_bytes(bytes).unwrap();
+        let dt = file.dataset("counts").unwrap().raw_datatype().unwrap();
+        assert!(
+            matches!(
+                dt,
+                Datatype::FixedPoint {
+                    size: 4,
+                    signed: true,
+                    ..
+                }
+            ),
+            "{dt:?}"
+        );
+        // The full type pairs with read_selection's bytes.
+        let raw = file
+            .dataset("counts")
+            .unwrap()
+            .read_selection(&Selection::All)
+            .unwrap();
+        assert_eq!(
+            clawhdf5_format::data_read::read_as_i64(&raw, &dt).unwrap(),
+            vec![10, 20, 30]
+        );
+    }
+
     #[test]
     fn root_group_datasets() {
         let bytes = make_simple_file();

crates/clawhdf5/src/reader.rs

@@ -416,6 +416,15 @@ impl<'f> Dataset<'f> {
         Ok(classify_datatype(&dt))
     }
 
+    /// Returns the dataset's full datatype as stored in the file (byte order,
+    /// string padding, compound layout, ...), with a committed datatype
+    /// resolved. Use it with the `clawhdf5_format::data_read` converters on
+    /// the bytes [`read_selection`](Self::read_selection) returns, for types
+    /// the typed `read_*` methods do not cover.
+    pub fn raw_datatype(&self) -> Result<Datatype, Error> {
+        self.datatype()
+    }
+
     /// Read all data as `f64` values.
     pub fn read_f64(&self) -> Result<Vec<f64>, Error> {
         let dt = self.datatype()?;