fix: sum tree parent costs

[QuantumExplorer]

Issue being fixed or feature implemented

There were two issues being fixed in this PR.

The first is that sum items have variable cost. This is particularly a problem when updating the balance of an identity as we do not want added or removed bytes which would cause a headache for estimated costs. Now Sum Items always have the same cost (9 bytes). We chose 9 bytes because it represents the size of a i64::Max which is larger than the amount of credits possible in the system.

The second is that a sum tree was calculating if it was in a sum tree itself based on whether it was a sum item (it always was). This was leading to a nasty issue where GroveDb would be reporting that bytes were being removed from the system on update.

What was done?

How Has This Been Tested?

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone