Fix linter setup

[zcei]

Hej folks,

while I wanted to work on this library for a proposed fix, I realized that the current linter setup was not actually linting TypeScript files. (I've screwed up this globbing vs. --ext a couple times myself 😅 )

To make it easier to track the changes I've split up the work into multiple easy-to-review commits, and would recommend to not review chore: ESLint autofixes (0a5d8bd) as it exclusively enforces linting rules you've set up previously and they are tested by the ESLint autofix implementation.

The two biggest changes are replacing a single forEach with a for-of loop to fix no-unused-expressions and introducing a new innerComplexities variables to fix no-param-reassign.

[ivome]

Thanks for fixing the linter setup @zcei . While I was at it, I also set up prettier via #51 for automatic code formatting and got rid of all the custom linting rules in favor of the standard recommended ones to make it easier to contribute.

[zcei]

@ivome even better - I was considering introducing it as well, but decided against it to not bloat the changeset any further. Love to see it!