test: tighten waveform-collapse and knob-face rect assertions

Height-3 case pins the halfSpan clamp itself (height-4 passed pre-fix too); dropped the vacuous tall-rect mirror since min() is symmetric and wide already discriminates.

tests/test_knob_deck.cpp

@@ -395,12 +395,8 @@ static void testInKnobFaceUsesTheSmallerDimensionOnANonSquareRect() {
     CHECK(!inKnobFace(wide, cx, cy + 15));     // inside the RECT but outside the smaller-radius disc
     CHECK(!inKnobFace(wide, cx + 15, cy));     // same check along the wider axis
 
-    const Rect tall{0, 0, 20, 40};  // height > width: draws a 10px-radius disc, not 20px
-    const int tcx = tall.x + tall.width / 2;
-    const int tcy = tall.y + tall.height / 2;
-    CHECK(inKnobFace(tall, tcx, tcy));
-    CHECK(!inKnobFace(tall, tcx + 15, tcy));
-    CHECK(!inKnobFace(tall, tcx, tcy + 15));
+    // No mirrored tall{20,40} case: min() is symmetric in its two arguments, so a tall rect
+    // can't discriminate width/2 from min(w,h)/2 any differently than wide already does.
 }
 
 static void testEmptyDeck() {