Typescript config parity with Browsertrix repo (#289)

Follow-up from #288 

This matches the strictness rules with the Browsertrix repo,
specifically `noImplicitAny`, and then adds `// @ts-expect-error`s to
suppress existing errors this change raises. This'll help us keep code
quality high moving forward.

Going to just directly merge this once it passes CI; as with #288, this
doesn't change any code, just comments.

src/loader.ts

@@ -199,7 +199,6 @@ You can select a file to upload from the main page by clicking the 'Choose File.
       }
       // todo: too special case?
       if (sourceUrl!.startsWith("proxy:") && extraConfig?.recording) {
-        // @ts-expect-error - TS2322 - Type '"recordingproxy"' is not assignable to type 'undefined'.
         type = "recordingproxy";
       }
     }