On torspec!40, Mike says:

    I don't think there is a practical difference here. As per
    Section 2.4.5, if 60 seconds is not enough and causes the
    liveness test to fail due to too many timeouts, we will double
    the initial timeout.

This makes our behavior the same as C tor.

The C Tor implementation doesn't do this, and Mike says:

   I think it is a reasonable enough assumption that if Tor has
   restarted, this kind data is no longer fresh enough to be
   accurate for this purpose. This is also only 20 circuits here,
   and typical timeouts are now around 1-2 seconds or less.. So a
   restarted client with a timeout that is too low for a new
   internet connection will figure this out pretty quickly. I think
   that is OK.

(from torspec!40)

Now that we have const generics, we can use them.  We can also avoid
an extra clone in the implementation for [u8; N].

Nothing in our codebase requires that we use Reader or Writer on a
GenericArray holding anything other than u8, so I've switched back
to the more efficient implementation there.

I've added a fuzzer case for the new method, but apparently rustc nightly isn't working too
well with fuzzers for me; I'm going to try it tomorrow.

(The nightly version of clippy now includes macros for its
missing_docs_in_private_items lint.)

This will cause some pain for now, but now is really the best time
to do this kind of thing.