Linter fixes to umdp3 checker

[r-sharp]

PR Summary

Sci/Tech Reviewer: @Pierre-siddall
Code Reviewer:

While the previous umdp3 checker was being reviewed, I concentrated on some partial refactors mostly to reduce the number of 'problems' highlighted by the internal linter(s) in VSCode.

This branch contains those changes, but does not actually affect running the code.
I'm partially putting this into PR now to engage with @Pierre-siddall for a discussion about the OO "desighn" and perhaps to get answers to why some of these changes were required to satisfy linters when the code ran and I'm not sure what the linter is requesting is actually desired.
Especially the requirement of an init method in the 'abstract class' - although I now suspect the abstract class itself is no longer required, I'd like to know why an init method was required by the linter(s)

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• This change has been tested appropriately (please describe)

Security Considerations

• I have reviewed my changes for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• Code quality standards have been met
• Tests are adequate and have passed
• Security considerations have been addressed
• Performance impact is acceptable

[r-sharp]

Well, that went badly - this is 'supposed' to be an update to the previous PR, but it seems to be listing ALL the files touched as new, including a bunch of files that shouldn't be tracked at aLL and is generally just a complete disaster.
Bring back FCM - all is forgiven...