…ice on TypeError

_tp_cache falls back to calling the wrapped function directly when the
arguments are unhashable, which it detected by catching TypeError from the
lru_cache lookup.  A TypeError raised by the wrapped function itself was
caught the same way, so with hashable arguments the function ran once inside
the cache, was caught, and then ran a second time through the fallback before
the error propagated.  This was reachable through the public API, for example
typing.List[int, str] evaluated its whole __getitem__ twice.

Only fall back when the arguments really are unhashable, by rebuilding the
same cache key lru_cache uses, and re-raise otherwise so the function is not
run a second time.

…riations

Both tests exercised the same positional and keyword call variations but
handled them inconsistently: one cleared the calls list between them, the
other asserted the combined result.  Loop over the variations with subTest
and clear the list each iteration so each variation is asserted in isolation.