firmware/actions: reuse isError from utils

Remove duplicate isError function.

src/firmware/actions.ts

@@ -4,6 +4,7 @@
 import { FirmwareReaderError, HubType } from '@pybricks/firmware';
 import { createAction } from '../actions';
 import { Hub } from '../components/hubPicker';
+import { isError } from '../utils';
 
 export enum MetadataProblem {
     Missing = 'metadata.missing',
@@ -144,16 +145,6 @@ export const didFinish = createAction(() => ({
     type: 'flashFirmware.action.didFinish',
 }));
 
-function isError(err: unknown): err is Error {
-    const maybeError = err as Error;
-
-    return (
-        maybeError !== undefined &&
-        typeof maybeError.name === 'string' &&
-        typeof maybeError.message === 'string'
-    );
-}
-
 // FIXME: get rid of this monstrosity
 
 const didFailToFinishType = 'flashFirmware.action.didFailToFinish';

src/utils/index.ts

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: MIT
-// Copyright (c) 2020-2022 The Pybricks Authors
+// Copyright (c) 2020-2026 The Pybricks Authors
 
 /**
  * Asserts that an assumption is true. This is used to detect programmer errors
@@ -43,7 +43,7 @@ export function hex(n: number, pad: number): string {
     return `0x${n.toString(16).padStart(pad, '0')}`;
 }
 
-function isError(err: unknown): err is Error {
+export function isError(err: unknown): err is Error {
     const maybeError = err as Error;
 
     return (