tests/bench: Add testcases for lookup in 5-el instance and namedtuple.
... and we have not that bad mapping type after all - lookup time is ~ the same as in one-attr instance. My namedtuple implementation on the other hand degrades awfully. So, need to rework it. First observation is that named tuple fields are accessed as attributes, so all names are interned at the program start. Then, really should store field array as qstr, and do quick 32/64 bit scan thru it.