Upgrade Vitest to 4.0.16 and convert to inline snapshots

[Copilot]

Modernizes test infrastructure per maintainer request.

Changes

• Vitest: 2.0.5 → 4.0.16
• Snapshots: Converted from external files to inline snapshots
  • Changed toMatchSnapshot() → toMatchInlineSnapshot() in getRepositoryInfo tests
  • Removed __snapshots__/ directory

The inline snapshots are now embedded directly in the test file:

expect(getRepositoryInfoAdapter('https://github.com/owner/repo/tree/main/src')).toMatchInlineSnapshot(`
  {
    "name": "repo",
    "nameWithOwner": "owner/repo",
    "owner": "owner",
    "path": "tree/main/src",
    "pathParts": [
      "tree",
      "main",
      "src",
    ],
  }
`);

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