fix(ui): invocation parsing for optional enum fields

For example:
```py
my_field: Literal["foo", "bar"] | None = InputField(default=None)
```

Previously, this would cause a field parsing error and prevent the app from loading.

Two fixes:
- This type annotation and resultant schema are now parsed correctly
- Error handling added to template building logic to prevent the hang at startup when an error does occur

Author: psychedelicious

invokeai/frontend/web/src/features/nodes/util/schema/buildFieldInputTemplate.ts

@@ -682,7 +682,7 @@ const buildEnumFieldInputTemplate: FieldInputTemplateBuilder<EnumFieldInputTempl
     if (filteredAnyOf.length !== 1 || !isSchemaObject(firstAnyOf)) {
       options = [];
     } else {
-      options = firstAnyOf.enum ?? [];
+      options = firstAnyOf.const ? [firstAnyOf.const] : (firstAnyOf.enum ?? []);
     }
   } else if (schemaObject.const) {
     options = [schemaObject.const];

invokeai/frontend/web/src/features/nodes/util/schema/parseSchema.ts

@@ -161,8 +161,15 @@ export const parseSchema = (
           fieldType.batch = true;
         }
 
-        const fieldInputTemplate = buildFieldInputTemplate(property, propertyName, fieldType);
-        inputsAccumulator[propertyName] = fieldInputTemplate;
+        try {
+          const fieldInputTemplate = buildFieldInputTemplate(property, propertyName, fieldType);
+          inputsAccumulator[propertyName] = fieldInputTemplate;
+        } catch {
+          log.error(
+            { node: type, field: propertyName, schema: parseify(property) },
+            'Problem building input field template'
+          );
+        }
 
         return inputsAccumulator;
       },
@@ -226,9 +233,16 @@ export const parseSchema = (
           fieldType.batch = true;
         }
 
-        const fieldOutputTemplate = buildFieldOutputTemplate(property, propertyName, fieldType);
+        try {
+          const fieldOutputTemplate = buildFieldOutputTemplate(property, propertyName, fieldType);
+          outputsAccumulator[propertyName] = fieldOutputTemplate;
+        } catch {
+          log.error(
+            { node: type, field: propertyName, schema: parseify(property) },
+            'Problem building output field template'
+          );
+        }
 
-        outputsAccumulator[propertyName] = fieldOutputTemplate;
         return outputsAccumulator;
       },
       {} as Record<string, FieldOutputTemplate>