fix(editor): handle footnote reference immediately follow URLs when importing markdown (#12449)

Closes: [BS-3525](https://linear.app/affine-design/issue/BS-3525/markdown-adapter-紧跟着链接的-footnote-reference-会被识别成链接的一部分)

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

## Summary by CodeRabbit

- **New Features**
  - Improved handling of footnote references that immediately follow URLs in markdown, ensuring correct spacing and parsing.
- **Bug Fixes**
  - Footnote references after URLs are now parsed correctly, preventing formatting issues.
- **Tests**
  - Added comprehensive test suites to verify footnote reference preprocessing and markdown conversion.
- **Chores**
  - Introduced Vitest as a development dependency and added a dedicated test configuration for the footnote module.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/inlines/footnote/package.json

@@ -33,6 +33,9 @@
     "yjs": "^13.6.21",
     "zod": "^3.23.8"
   },
+  "devDependencies": {
+    "vitest": "3.1.3"
+  },
   "exports": {
     ".": "./src/index.ts",
     "./view": "./src/view.ts",