chore: convert from jest to vitest v4.1.0

[Copilot]

Summary

Migrates the test framework from Jest (v30) to Vitest (v4.1.0), the latest version.

Changes

Dependencies

• Removed: jest (^30.1.3), ts-jest (^29.1.4), @types/jest (^30.0.0)
• Added: vitest (^4.1.0), @vitest/coverage-v8 (^4.1.0)
• Removed test-exclude override from package.json (was only needed by Jest's coverage tooling)

Configuration

• Added vitest.config.ts with equivalent settings:
  • globals: true — provides test, describe, it, test.each globals (matching Jest behavior)
  • include: ["**/*[tT]est.ts"] — same test file matching pattern
  • testTimeout: 100000 — same 100s timeout
  • coverage.enabled: true — same as Jest's collectCoverage: true
• Removed jest config section from package.json
• Updated ts.test script from jest to vitest run

TypeScript Configuration

• Added "types": ["vitest/globals"] to tsconfig.json (replaces @types/jest)
• Added "skipLibCheck": true (needed because vitest's type declarations use modern exports that require node16/bundler module resolution, while this project uses legacy commonjs module resolution)
• Added vitest.config.ts to exclude (required because rootDir is ./src)
• Added vitest.config.ts to eslint ignores

Source Change

• src/index.ts: Converted require("./lib/util/constants") to export { Constants } from "./lib/util/constants" — vitest's ESM-based module resolution doesn't support bare require() calls to TypeScript source files without extensions

Verification

• ✅ npm run tsc — builds successfully
• ✅ npm run lint — no warnings
• ✅ npm run prettier — all files formatted
• ✅ npm run ts.test — 5/5 non-.NET tests pass (18 tests that require dotnet DLLs fail as expected in this environment, same as with Jest)
• ✅ No security vulnerabilities (CodeQL clean)

Migration Notes

• No test files were modified — all tests use standard test()/describe()/it() globals and Node.js assert module, which are compatible between Jest and Vitest
• The test.each() API used in incompatiblePropertiesTest.ts works identically in Vitest