error: extend ErrorMessage & helpers for improved ergonomics

- added isRawError helper
- added catchErrorString helper to convert any error to a string
- added checkGraphResponse to throw if error is present or data missing
- ErrorMessage now supports wrapping multiple errors ergonomically

src/lib/index.ts

@@ -67,7 +67,14 @@ export {
 	ToolbarGroup,
 	Toolbar
 } from './Toolbar';
-export { type GraphError, type RawError, ErrorMessage } from './error';
+export {
+	type GraphError,
+	type RawError,
+	isRawError,
+	catchErrorString,
+	checkGraphResponse,
+	ErrorMessage
+} from './error';
 export {
 	NavigationItem,
 	NavigationManager,