Unit tests for ipairs and pairs, as well as changing how they handle null. ipairs now breaks at first nil value, pairs skips it

UpsilonTests/StandardLibraryTests/BasicFunctionsTests.cs

@@ -29,7 +29,7 @@ namespace UpsilonTests.StandardLibraryTests
         public void IPairsTest()
         {
             const string input = @"
-arr = {100, 56, 28}
+arr = {100, 56, 28, nil, 100}
 value = 0
 for key, val in ipairs(arr) do
     value = value + val
@@ -56,5 +56,22 @@ return tonumber(""100"")
             Assert.Equal(100, result);
         }
 
+        [Fact]
+        public void PairsTest()
+        {
+            const string input = @"
+arr = {100, 56, 28, nil, 100}
+value = 0
+for key, val in pairs(arr) do
+    value = value + val
+end
+return value
+";
+            var script = new Script(input, BoundScope, StaticScope);
+            Assert.Empty(script.Diagnostics.Messages);
+            var result = script.Evaluate<long>();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal(284, result);
+        }
     }
 }