Convert tests to TypeScript and use Vitest with coverage

[tomkp]

Summary

• Migrates test files from JavaScript to TypeScript with proper type annotations
• Replaces Node.js built-in test runner with Vitest for modern testing features
• Adds code coverage using @vitest/coverage-v8
• Adds vitest.config.ts with text, html, and lcov reporters
• Updates package.json with new test scripts
• Removes PC/SC library dependency from CI workflow (no longer needed without smartcard)

Test Coverage

File               | % Stmts | % Branch | % Funcs | % Lines
-------------------|---------|----------|---------|--------
All files          |   92.98 |      100 |   86.66 |   92.98
 command-apdu.ts   |     100 |      100 |     100 |     100
 iso7816-app.ts    |   86.36 |      100 |   66.66 |   86.36
 response-apdu.ts  |   95.45 |      100 |   92.85 |   95.45

Test plan

• All 35 tests pass with npm test
• Coverage report generates with npm run test:coverage
• TypeScript types are correct
• ESLint and Prettier pass

Fixes #34