Extract divisor validator and rename legacy CPU prime helper

PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs

@@ -263,7 +263,7 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
             {
                 ulong candidate = (ulong)nextDivisor128;
 
-                if (CandidatePassesHeuristics(localRemainder10, localRemainder8, localRemainder3, localRemainder5, localRemainder7, localRemainder11, lastDigit))
+                if (DivisorGenerator.IsValidDivisor(localRemainder10, localRemainder8, localRemainder3, localRemainder5, localRemainder7, localRemainder11, lastDigit))
                 {
                     filteredStorage[filteredCount++] = candidate;
                 }
@@ -378,38 +378,6 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester : IMersenneNumberDiv
         return computedCycle;
     }
 
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static bool CandidatePassesHeuristics(
-        byte remainder10,
-        byte remainder8,
-        byte remainder3,
-        byte remainder5,
-        byte remainder7,
-        byte remainder11,
-        LastDigit lastDigit)
-    {
-        const ushort DecimalMaskWhenLastIsSeven = (1 << 3) | (1 << 7) | (1 << 9);
-        const ushort DecimalMaskOtherwise = (1 << 1) | (1 << 3) | (1 << 9);
-
-        ushort decimalMask = lastDigit == LastDigit.Seven ? DecimalMaskWhenLastIsSeven : DecimalMaskOtherwise;
-        if (((decimalMask >> remainder10) & 1) == 0)
-        {
-            return false;
-        }
-
-        if (remainder8 != 1 && remainder8 != 7)
-        {
-            return false;
-        }
-
-        if (remainder3 == 0 || remainder5 == 0 || remainder7 == 0 || remainder11 == 0)
-        {
-            return false;
-        }
-
-        return true;
-    }
-
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private static byte AddMod(byte value, byte delta, byte modulus)
     {