Description of change

Correctly handle tx cost arithmetic overflows in shared object congestion tracker. Upper bound max_accumulated_txn_cost_per_object_in_commit is allowed to be u64::MAX.

Links to any relevant issues

Fixes #4177.

Type of change

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• Bug fix (a non-breaking change which fixes an issue)

How the change has been tested

Added unit test to cover edge cases.

Change checklist

Tick the boxes that are relevant to your changes, and delete any items that are not.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes