[SeiDB] Fix PebbleDB Iterator Issue

[Kbhat1]

Describe your changes and provide context

• Fix for PebbleDB Iterator issue
• Previously, the mvcc iterator would loop indefinitely when it reached a key that was greater than the iterator version specified and go back to a previous key
• Catch the scenario where iterator moves back to previous key and move it forward to avoid a loop

Testing performed to validate your change

• Tested and repro'd error on node

Before fix:

After fix:

[yzang2019]

We should add a test for reverse iteration as well

[Kbhat1]

Yea there are a lot more unit tests that are going to be pushed