In it's current state, the MachineConfigNode (MCN) functionality is implemented through a series of complex functions, which can lead to confusion and a feeling of it being unmaintainable. Further, there are no unit tests for the feature, so adding or modifying functions is only tested through regression tests, which is the most expensive way to test all new changes.

Note that this task is for generally making transparent the need for refactoring this section of the codebase. However, it may be beneficial to break this into a spike and some stories, depending on the amount of effort this will take.

Done when:

• MCN functionality is refactored so it is more maintainable
  • Some functions need complexity decreased
  • The upgrade monitor may need to be fully re-written
• There are unit tests that cover edge cases for the MCN that can cheaper test modifications to the upgrade monitor

Additional context:

• Related GitHub comment: https://github.com/openshift/machine-config-operator/pull/5282#discussion_r2419874518 
• Related Slack thread: https://redhat-internal.slack.com/archives/GH7G2MANS/p1760100044107129?thread_ts=1759779460.596649&cid=GH7G2MANS