Fix for setting of BG Targets

[Sjoerd-Bo3]

Implemented the iAPS fix https://github.com/Artificial-Pancreas/iAPS/pull/715/files that closes Issue #318

[marionbarker]

Summary

I confirm Issue #318 is fixed with this patch

Testing

Tested by applying patch to alpha commit 82f2d01a

• built on existing Trio, SE running iOS 17.5.1
• units already mmol/L from testing the issue earlier (see comment)
  • modify target, save, go to settings, return to target screen:
    • choose 6.0; final 6.0
    • choose 6.1; final 6.1
    • choose 6.2; final 6.2
    • choose 4.0, final 4.0
    • choose 10.0, final 10.0

[dnzxy]

Bandaid fix for now, we generally a more thought out handling of mmol values; handle everything in mg/dl and only display in mmol.

This fixes #318 and LGTM. Merging with 3 approvals.