make eslint scream about promises, then fix all lints

also rewrite a bunch of test suites from using done callbacks to using
async functions - it's way too easy to forget about a .catch() clause

src/routes/getVideoLabel.ts

@@ -122,7 +122,7 @@ function chooseSegment<T extends DBSegment>(choices: T[]): FullVideoSegmentVideo
         return {
             segments: transformDBSegments(choices),
             hasStartSegment
-        }
+        };
     }
     // if locked, only choose from locked
     const locked = choices.filter((segment) => segment.locked);