Extra decimal support for TPC-H Q18 (#261)

Regrettably the query is still too slow...

Would like a sanity check on this in any case.

Won't merge until unnest-exists is merged

optd-core/src/nodes.rs

@@ -211,7 +211,16 @@ impl Value {
                 }
                 _ => panic!("{self} could not be converted into an Date32"),
             }),
-            _ => unimplemented!("Have not implemented convert_to_type for DataType {typ}"),
+            DataType::Decimal128(_, _) => Value::Decimal128(match self {
+                // TODO: Should we be ignoring the scale and precision here?
+                Value::Int128(i128) => *i128,
+                Value::Int64(i64) => (*i64).into(),
+                Value::Int32(i32) => (*i32).into(),
+                _ => panic!("{self} could not be converted into an Decimal128"),
+            }),
+            _ => unimplemented!(
+                "Have not implemented convert_to_type from {self} for DataType {typ}"
+            ),
         }
     }
 }

optd-datafusion-repr/src/plan_nodes/predicates/constant_pred.rs

@@ -46,6 +46,7 @@ impl ConstantType {
             Value::Int64(_) => ConstantType::Int64,
             Value::Float(_) => ConstantType::Float64,
             Value::Date32(_) => ConstantType::Date,
+            Value::Decimal128(_) => ConstantType::Decimal,
             _ => unimplemented!("get_data_type_from_value() not implemented for value {value}"),
         }
     }