Use per-fraction reference doses in quality indicators

[acsevillam]

Bug description

Quality indicators mixed per-fraction dose cubes with total prescription/objective doses in some analysis paths.

Approach

This PR keeps canonical quality indicators in per-fraction dose units and adds explicit conversion helpers for display/evaluation in total dose when requested.

Open Questions and/or Concerns

• Confirm the per-fraction convention is the desired canonical representation for plan analysis outputs.

References

None.

[wahln]

This is nice and makes it more consistent. The per fraction thing is anyway something that is very strongly debated among us, so the conversion function for the modes is also good.

I just realized you opened the PR onto dev_varRBErobOpt - could you rebase/reopen onto dev? dev_varRBErobOpt was merged into dev quite some time ago. If yes, please close this PR when the new one is reopened.

[acsevillam]

Closing this PR in favor of #909.

The new PR preserves the original intent of #904: quality indicators are kept canonical in dose per fraction, with explicit conversion applied only for evaluation and display. PR #909 adapts this behavior to the current dev codebase.