Major Description
Found there are "many" KeyValueIterator implemented instances don't explicitly get closed, which will cause resource leak.
From the java doc in KeyValueIterator:
* Users must call its {@code close} method explicitly upon completeness to release resources
This issue mostly happen in tests because we usually query state store to get result iterator, and then do verification, but forgot close it. This issue also appear in the example code in our developer guide docs.
I'll use try-with-resource to fix them. To avoid huge PR created, I split this bug into 3 sub-tasks.