vtable BestIndex callback missing colUsed input

[theimpostor]

struct sqlite3_index_info includes a mask of all column indexes used: https://github.com/mattn/go-sqlite3/blob/7658c06970ecf5588d8cd930ed1f2de7223f1010/sqlite3-binding.h#L7487

This should be included as a parameter to the BestIndex virtual table callback.