This PR fixes over 1,000 type errors across the monorepo by addressing root causes in `tsconfig.json` configurations and the `@google/gemini-cli-core` build process.
### Key Changes:
- **Upgraded `lib` to `ES2023`** in `packages/test-utils` and `packages/vscode-ide-companion` to support modern features like `Error.cause` and `Object.hasOwn`, aligning them with the root configuration.
- **Removed deprecated `baseUrl`** from `packages/core/tsconfig.json` and converted absolute-style imports in tests to relative imports.
- **Stabilized `@google/gemini-cli-core` build** to ensure `.d.ts` files are correctly generated, resolving `TS6305` errors in dependent packages.
- Verified that all workspaces and top-level test suites now pass `npm run typecheck`.
These changes restore the intended type health of the project and ensure consistent build behavior across different TypeScript versions.
cc @gundermanc
Labels: bot-fix
gemini-cli[bot]