Export types for EnvVars, MockedEnvOptions

[junhoyeo]

Background

I needed to wrap the mockedEnv function again like the following:

// Some outer scope
let restoreEnv: RestoreFn = () => {};
afterEach(() => {
  restoreEnv();
});

const mockEnvironmentVariables = (variables: EnvVars) => {
   ...
  restoreEnv = mockedEnv(variables);
}

The type interface EnvVars isn't exported from the module; it has to be defined in my codebase again, hurting my context.

Changes

• I made changes so this library exports the interface EnvVars so it can be used outside.
• Also exported the MockedEnvOptions for similar needs.

Notes

• I'll be delighted if you decide to merge this PR and release an update soon 🙇