fix(feedback): Require minimum sample count before triggering shake

The 75% bit-shift formula degrades at low sample counts (e.g. 33% at
3 samples). With SENSOR_DELAY_NORMAL (~5Hz) the queue may hold only
3 samples in 0.5s. Adding a MIN_QUEUE_SIZE guard ensures the threshold
stays accurate and prevents false triggers from walking.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: romtsn

sentry-android-core/src/main/java/io/sentry/android/core/SentryShakeDetector.java

@@ -201,6 +201,7 @@ private void purge(final long cutoff) {
     boolean isShaking() {
       return newest != null
           && oldest != null
+          && sampleCount >= MIN_QUEUE_SIZE
           && newest.timestamp - oldest.timestamp >= MIN_WINDOW_SIZE_NS
           && acceleratingCount >= (sampleCount >> 1) + (sampleCount >> 2);
     }