fix(editor): unify file size formatting method (#12444)

Closes: [BS-3524](https://linear.app/affine-design/issue/BS-3524/统一文件大小单位，与-af-一致)

![Screenshot 2025-05-22 at 15.09.41.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/8ypiIKZXudF5a0tIgIzf/ddb6fa38-243f-4e65-b572-d476e3771d74.png)

![Screenshot 2025-05-22 at 15.09.48.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/8ypiIKZXudF5a0tIgIzf/5d182332-4d0a-419a-b206-df58552fe740.png)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **Refactor**
  - Updated file size formatting throughout the app to use a new, consistent utility for displaying file sizes.
  - Improved clarity and uniformity of file size information in attachments, images, and related notifications.
  - Enhanced type support to explicitly allow null values for file size descriptions.
- **Bug Fixes**
  - Adjusted file size display in tests to match updated formatting standards.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

tests/blocksuite/e2e/attachment.spec.ts

@@ -143,7 +143,7 @@ test('can insert attachment from slash menu', async ({ page }, testInfo) => {
   await waitLoading();
 
   expect(await getName()).toBe(FILE_NAME);
-  expect(await getSize()).toBe('45.8 kB');
+  expect(await getSize()).toBe('44.73KB');
 
   expect(await getPageSnapshot(page, true)).toMatchSnapshot(
     `${testInfo.title}.json`
@@ -285,7 +285,7 @@ test(`support dragging attachment block directly`, async ({
   await waitLoading();
 
   expect(await getName()).toBe(FILE_NAME);
-  expect(await getSize()).toBe('45.8 kB');
+  expect(await getSize()).toBe('44.73KB');
 
   expect(await getPageSnapshot(page, true)).toMatchSnapshot(
     `${testInfo.title}_1.json`