perf: make `clearfilecache` helper work with any object If the object is not a localrepo, it won't have an `unfiltered` method (and won't need one).

perf: move some of the perftags benchmark to the setup function Creating fresh objects and clearing the cache should not be part of the timing. before: ! wall 0.020851 comb 0.020000 user 0.020000 sys 0.000000 (median of 138) after: ! wall 0.018740 comb 0.020000 user 0.020000 sys 0.000000 (median of 141)