Fix inconsistencies in node contracts states

[sameh-farouk]

Description

• A defensive check has been added to ensure that node contracts verify the state of the associated rent contract before transitioning to the created or resumed state.
• When a rent contract attempts to resume a node contract, it now checks for any unsettled funds associated with that node contract.
• The deletion of rent contracts is now delayed until all associated node contracts (with incurred costs) are independently billed and deleted. This ensures that no active node contracts have reserved balances before proceeding with rent contract deletion.
• State transitions from gracePeriod(x) to gracePeriod(y) are now blocked to prevent improper state changes.

Related Issues:

https://github.com/threefoldtech/tfchain/issues/1002

Checklist:

Please delete options that are not relevant.

• [x] I have added tests to cover my changes.
• [X] My commits follow this conventional commits guide.

[sameh-farouk]

@renauter Thank you for your thoughtful review. I’ve addressed most of your comments.

I also appreciate the suggestion to add more assertions, but I believe these extra checks go beyond the scope of these test cases. The existing assertions already verify the core functionality being fixed, and adding more may detract from the specific focus of the test.