feat: version upgrade diagnostics and quick fix

[9romise]

Part of #2
This PR add a diagnostic rule that detects outdated package versions and offers a quick fix to upgrade:

• For stable versions: hints when a newer latest is available
• For prerelease versions: hints when a newer version in the same channel exists (e.g., beta.1 → beta.3), or when a stable release supersedes it

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds an upgrade diagnostics feature: a new npmx.diagnostics.upgrade configuration (default true), a diagnostic rule that emits hints when newer package versions or matching prerelease tags exist, a CodeAction provider that offers quick-fix updates, and a new UPGRADE_MESSAGE_PREFIX constant. It moves version-handling logic out of src/utils/package.ts into a new src/utils/version.ts, introducing parseVersion, formatVersion, getPrereleaseId, and lt, and updates imports across consumers. Tests were adjusted to cover the new version utilities.

Possibly related PRs

• refactor: enhance version parsing with protocol support and validation #30: Refactors the version-parsing API and migrates protocol-aware parsing from src/utils/package.ts to src/utils/version.ts, aligning caller updates.
• feat(completion): support 'npm:'-prefixed versions #29: Modifies the parseVersion/formatVersion surface and updates their usage across completion, diagnostics and hover providers.

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description check	✅ Passed	The pull request description accurately relates to the changeset, describing the diagnostic rule for detecting outdated packages and offering quick fixes to upgrade.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch feat/check-upgrade

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Actionable comments posted: 2

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Actionable comments posted: 1