fix: accept FixedSizeList dtype when deserializing ListValue scalars

Scalar serialization writes ScalarValue::Tuple as a protobuf ListValue
regardless of whether the dtype is List or FixedSizeList, but
list_from_proto only accepted List. Since #8667 made constant detection
unconditional in the cascading compressor, a constant FixedSizeList
column (e.g. a UUID stored as fixed_size_list(u8)[16]) is written as a
ConstantArray whose scalar metadata then fails to deserialize on read:

    expected List dtype for ListValue, got fixed_size_list(u8)[16]

Scalar validation already handles FixedSizeList + Tuple (including the
size check), so deserialization was the only gap.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Frederic Branczyk <fbranczyk@gmail.com>

Author: brancz

vortex-array/src/scalar/proto.rs

@@ -441,9 +441,13 @@ fn list_from_proto(
     dtype: &DType,
     session: &VortexSession,
 ) -> VortexResult<ScalarValue> {
-    let element_dtype = dtype
-        .as_list_element_opt()
-        .ok_or_else(|| vortex_err!(Serde: "expected List dtype for ListValue, got {dtype}"))?;
+    let element_dtype = match dtype {
+        DType::List(edt, _) => edt,
+        DType::FixedSizeList(edt, _, _) => edt,
+        _ => {
+            vortex_bail!(Serde: "expected List or FixedSizeList dtype for ListValue, got {dtype}")
+        }
+    };
 
     let mut values = Vec::with_capacity(v.values.len());
     for elem in v.values.iter() {