chore: update dev dependencies

[lukecotter]

📝 PR Overview

Updates dev tooling dependencies, most notably @types/vscode to ~1.100.0. The new VS Code types add a required encoding property to TextDocument, which broke our Jest vscode mock; this also hardens that mock so future type drift is caught in one place rather than across every call site.

🛠️ Changes made

• Bump dev deps: @types/vscode ~1.99.1 → ~1.100.0, plus @swc/core, eslint, rolldown, typescript-eslint, lint-staged and related tooling.
• Type the createMockTextDocument factory against the real vscode.TextDocument via a type-only import (erased at runtime, so it doesn't clash with the Jest vscode module mapping), replacing the hand-written MockTextDocument interface that silently drifted.
• Add the newly-required encoding property to the mock; cast the four methods returning our simplified Position/Range/TextLine mocks so the object literal stays assigned to TextDocument (missing-property drift now fails once, at the factory).

🧩 Type of change (check all applicable)

• 🐛 Bug fix - something not working as expected
• ✨ New feature – adds new functionality
• ♻️ Refactor - internal changes with no user impact
• ⚡ Performance Improvement
• 📝 Documentation - README or documentation site changes
• 🔧 Chore - dev tooling, CI, config
• 💥 Breaking change

🔗 Related Issues

✅ Tests added?

• 👍 yes
• 🙅 no, not needed
• 🙋 no, I need help

📚 Docs updated?

• 🙅 not needed

Test plan

• pnpm lint
• pnpm test (folding + language detector suites pass: 23/23)