Switch to pnpm and run tests against edge-runtime.

[leerob]

This PR runs the Jest test suite against the Edge Runtime: a toolkit for developing and testing against Edge environments (like Edge Functions).

For example, the following test would pass:

// jest --env node
// ✅ Pass
it('should return the correct value', () => {
  let val = eval('2 + 2');
  expect(val).toBe(4);
});

The following test would fail when using the Edge Runtime:

// jest --env @edge-runtime/jest-environment
// ❌ Fail
// Error name:    "EvalError"
// Error message: "Code generation from strings disallowed for this context"
it('should return the correct value', () => {
  let val = eval('2 + 2');
  expect(val).toBe(4);
});

All tests inside this repository pass against both environments. This PR also does some housekeeping:

• Switches to pnpm
• Updates the README copyright year