optimize a query only once when binding exists

[eurekaka]

Enhancement

Currently, we would optimize a query firstly, and build a hint from the plan, then check if the hint matches any binding in the cache, if not, we use the bindings for another round of optimize. This would make a query be optimized several times if the hint in the binding is not normalized, and if the query contains uncorrelated subqueries, this optimization process would consume a lot of time.