options refactor: OptionKey initialisation is too slow

[bruchar1]

The generate_target function of ninja backend takes 55s for me on master, but 84s on the optionrefactors branch.

It seems it spends a lot of time constructing OptionKey objects. I think the @total_ordering decorator is one cause of that. Removing it allowed to reduce time to 64s in my profile.

Also, the __eq__ operator should use the _hash member instead of comparing tuples.