doc: add caveats and example to crypto.timingSafeEqual
#41507 recently added documentation about an error case for crypto.timingSafeEqual
, but even with that addition I think there are a few extra caveats to timingSafeEqual
's use that are worth mentioning. I've tried to be as clear as possible in this addition without going outside the scope of documentation for a single function (ie. into the realm of broader crypto best practices). I've also added a short example for the function.