Add exact-zero guards in various classes to prevent division by zero errors

lib/statistics/mode/Mode.cs

@@ -307,6 +307,7 @@ public sealed class Mode : AbstractBase
 
         for (int i = 1; i < count; i++)
         {
+            // skipcq: CS-R1077 - Exact-equality required: mode detection counts identical values in a sorted array; epsilon would merge distinct prices
             if (sorted[i] == sorted[i - 1])
             {
                 currentFreq++;

lib/statistics/spearman/Spearman.cs

@@ -226,6 +226,7 @@ public sealed class Spearman : AbstractBase
                 {
                     countSmaller++;
                 }
+                // skipcq: CS-R1077 - Exact-equality required: Spearman tie-detection needs bit-identical values; epsilon would create false ties
                 if (vj == vi)
                 {
                     countEqual++; // includes self