util: throw if unreachable TypedArray checking code is reached

If a comparison code path that is supposed to be unreachable is reached,
throw. Add a c8 comment to ignore coverage for the line, as it
should be unreachable.

PR-URL: https://github.com/nodejs/node/pull/31737


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>