Variable numeric set with units

Changes in 1.9

• This version is compatible with Moodle 5.0.


• Fixed coding style issues.


• Defined excluded hash fields and implemented conversion of legacy backup data
  to align with new question data format (per MDL-83541).


• Resolved warning: undefined array key text in spacesfeedback.


• Fix backup and restore tests to run synchronously in Moodle 4.4.


• Fix test question configurations.


• Changed the unit class to be autoloaded, to prevent issues during question data unserialization.


• Added a new option to the question editing form: "If scientific notation is not formatted correctly",
  allowing users to choose whether to accept a space between the number and unit as a valid response.


• Fix a bug where editing question with multiple answers, caused some of the answers being lost.


• Improved handling of number formatting on the question editing form.


• Added checks for empty variables to prevent save errors on the edit form.


• Automation test failures are fixed.