MeasureText runs for every sensor's Value/Min/Max on each update tick, and the
frequently-changing value strings miss the width cache, so it created and threw
away a WinUI TextBlock (with a native peer) on nearly every call. Reuse one
cached instance to avoid that per-tick allocation churn.
Not a leak fix — the GC reclaimed those elements fine; this just removes
needless allocation and CPU work from the update loop.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>