Add statistics to the fuzzer that countr how often certain expressions/functions are being tested

Currenlty we randomly select functions/Expressions when fuzzing. Once https://github.com/duckdb/duckdb_sqlsmith/issues/23 is merged, these percentages will be easy to change on the fly.

What might be cool to do next is to gather statistics to see what expressions and functions we are fuzzing.
Potentially there is a lot of skew right now and we don't know.
Would also be nice to see how many statements result in an Exception and how many get executed.