tests for  	zrangebylex, zrange, zlexcount, zincrby, zcount, zcard, zadd

Tests for the first few commands of sorted sets. Please review.

This util function is being used only two times.
Can you please make it a private method of `SortedSetCommandsMixin` (eg: `_convert_to_int_or_float`).

I am thinking on return values converters/decoders and I will come up with idea soon, so for now lets keep
such functions close to the code that uses them.