Relax ulong multiply-shift guards and refresh tests

PerfectNumbers.Core/ULongExtensions.cs

@@ -59,22 +59,12 @@ public static class ULongExtensions
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static int GetBitLength(this ulong value)
     {
-        if (value == 0UL)
-        {
-            return 0;
-        }
-
         return 64 - BitOperations.LeadingZeroCount(value);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ulong MultiplyShiftRight(ulong value, ulong multiplier, int shift)
     {
-        if (shift < 0)
-        {
-            throw new ArgumentOutOfRangeException(nameof(shift), "Shift must be non-negative.");
-        }
-
         UInt128 product = (UInt128)value * multiplier;
         return (ulong)(product >> shift);
     }
@@ -82,21 +72,6 @@ public static class ULongExtensions
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ulong MultiplyShiftRightShiftFirst(ulong value, ulong multiplier, int shift)
     {
-        if (shift < 0)
-        {
-            throw new ArgumentOutOfRangeException(nameof(shift), "Shift must be non-negative.");
-        }
-
-        if (shift == 0)
-        {
-            return MultiplyShiftRight(value, multiplier, 0);
-        }
-
-        if (shift >= 64)
-        {
-            return 0UL;
-        }
-
         ulong high = value >> shift;
         ulong mask = (1UL << shift) - 1UL;
         ulong low = value & mask;