Also solves a performance regression initially introduced by b6e8297e369f2dc4758bafe944e51efb8d1a2552,
primarily due to excessively mismatched load/store sizes causing less than optimal load-to-store forwarding.
Generally hash functions shouldn't throw exceptions. It's also a
requirement for the standard library-provided hash functions to not
throw exceptions.
An exception to this rule is made for user-defined specializations,
however we can just be consistent with the standard library on this to
allow it to play nicer with it.
While we're at it, we can also make the std::less specializations
noexcpet as well, since they also can't throw.
