Add benchmarks for complex type #458

This inspired by python/cpython#135233.

Unfortunately, we don't have any benchmarks for this builtin type, that opens door for possible speed regressions, just like for the decimal module (see python/cpython#144650).

Perhaps, even simple sin() benchmarks from the referenced pr would be better than nothing: python/cpython#135233 (comment) But I appreciate suggestions.

CC @tim-one