many features and fixes

Features:

• new Watch app with second "Big Number" screen - scroll or swipe down to see it
• new dynamic gauge dials for Watch app/complications to accurately show the user ranges
• changes to simplify Algorithm and Calibration types
  -- now the user can easily chose between Native (previously called Transmitter) algorithm and xDrip algorithm
  -- the default calibration type is now always Standard (single-point). The user must change manually to multi-point.
  -- explanations added at each stage of chaning algorithm/calibration type.
• Calibration type is disabled when using the native algorithm and the UI now makes this clear
• Smooth Libre Values option is moved from Developer settings to the Libre 2 bluetooth peripheral screen
• "Libre 2 Direct" is now renamed throughout the app to "Libre 2 EU" to prevent confusion with CA/US/AUS sensors
• When a transmitter is connected, but sensor values are yet to arrive, the app will now show "Waiting for data...".
• slope information added to BG Readings view
• added Bubble Nano support
• Dexcom Share upload now clearly indicates to the user the information required before it will start to work. To prevent users thinking they should be uploading data when the receiver s/n was missing etc
• the Contact Image will no longer delete the contact after disabling the function. This will prevent people losing updates after toggling on/off the option.
• a "Use High Contrast" option now exists for the Contact Image for people that use tinted/coloured watchfaces. It helps prevent the colours from looking washed-out.
• Contact Image will now work for follower modes, but will stay disabled (showing "OFF") if the background keep-alive is set to Disabled. This is to prevent users seeing out of date values with no indication that they are old.
• Live Activity is now no longer switchable for "Only when high, low etc" as the app can't generate Live Activities from the background so it was of little value. The UI now merges all functions into one single option (disabled, minimal, normal, large)

Fixes:

• LibreLinkUp Follower modified to work even when there is an empty Active Sensor response from server.
• fix for follower network icon in Watch app
• max Sensor lifetime is increased to 10.5 days for G7/ONE+ to take advantage of the grace period
• G6 sensor session will now autostart correctly in xDrip4iOS always if the sensor is started using the Dexcom app
• the sensor start date will automatically get hidden now until valid BG data is coming in after warm-up to prevent confusion with incorrect data.
• ensure Developer settings are automatically hidden always
• G6 transmitter runtime/temperature and resistance is completely removed from the UI to avoid confusion (not so relevant after G5)
• updates to REXML dependencies (from 3.2.8 to 3.3.6)
• observers in the bluetooth screen are dynamically created/destroyed to minimize crashes in <iOS18
• Xcode 16 compiler warnings fixed
• Watch app background updates > 12 hours ago are discarded upon opening the Watch app. This will prevent "freezing/scrolling" through very old data if somebody hasn't opened the Watch app in several days.
• changes to the delta display text for small delta changes (usually +0 or +-1) that sometimes didn't match due to rounding (@aug0211)
• mmol/L delta calculations are now processed in real converted values to avoid delta errors in mmol/L
• LibreLinkUp version updated to 4.12.0 (it will automatically update all users settings the first time it is run)
• the small system widget (iOS) will no longer show the keep-alive icon to save sp