Enable require-await eslint rule

[taoeffect]

Problem

Per #1052 (comment)

There are apparently several places where async is used to describe a function with no corresponding await.

This can create confusion as to what the return value is supposed to be (e.g. a promise or a raw value) and could lead to bugs.

Solution

Add require-await and fix all existing errors, making sure to double-check the return values are properly handled when async is removed.