Add jsdoc for `.toEqualTypeOf`

Closes #50

## This PR:

- [X] Fixes `.omit()` to work similarly to `Omit`. This was done in a
way that allows type hinting and intellisense to work without being too
strict.
  - [X] Resolves #53.

## This PR:

- [X] Adds inline documentation to everything inside of the library in
the form of JSDocs.

FYI @aryaemami59 I'm updating the lint setup to use eslint-plugin-mmkal
here. It might cause minor conflicts with your PR, but any lint errors
should be auto-fixable.

The new eslint-plugin-mmkal uses the flat config format so no more
`mmkal/` prefix on the various eslint-disables.

---------

Co-authored-by: Misha Kaletsky <[email protected]>

Another FYI @aryaemami59, I'm moving my repos gradually over from jest
to vitest. Figured this would be a good one to do since vitest uses
expect-type!

Adding the `vitest` dependency enables removing `jest`, `@types/jest`,
`ts-jest`, `jest.config.js` and the `globals_jest` eslint config.

---------

Co-authored-by: Misha Kaletsky <[email protected]>

## This PR:

  - [X] Resolves #63.

## This PR:

- [X] Adds `test-types` CI job to run `tsc` with different versions of
TypeScript.
  - [X] Updates `actions/checkout` usages to v4.
  - [X] Resolves #60.

---------

Co-authored-by: Misha Kaletsky <[email protected]>