refactor: NoTypeName should be only one instance

NewSource/Socordia.CodeAnalysis/AST/TypeNames/NoTypeName.cs

@@ -1,3 +1,8 @@
 namespace Socordia.CodeAnalysis.AST.TypeNames;
 
-public class NoTypeName : TypeName;
+public class NoTypeName : TypeName
+{
+    public static readonly NoTypeName Instance { get; } = new NoTypeName();
+
+    private NoTypeName() { }
+}

NewSource/Socordia.CodeAnalysis/Parsing/ParsePoints/Statements/VariableStatementParser.cs

@@ -11,7 +11,7 @@ public static AstNode Parse(TokenIterator iterator, Parser parser)
         var keywordToken = iterator.Prev;
 
         var isMutable = false;
-        TypeName? type = new NoTypeName();
+        TypeName? type = NoTypeName.Instance;
 
         Token mutableToken = null;
 

NewSource/Socordia.CodeAnalysis/Parsing/ParsePoints/TypeNameParser.cs

@@ -82,7 +82,7 @@ public static TypeName Parse(Parser parser)
             parser.AddError("Expected Identifier, TupleType or Function-Signature as TypeLiteral, but got " +
                 TokenIterator.GetTokenRepresentation(iterator.Current.Type));
 
-            typeNode = new NoTypeName();
+            typeNode = NoTypeName.Instance;
             iterator.NextToken();
         }
 

NewSource/SocordiaC/Compilation/Listeners/Body/Lowering/SwapLowerer.cs

@@ -17,7 +17,7 @@ public class SwapLowerer : Replacer<AstNode, BinaryOperatorExpression>
 
         //todo: implement a swap by introducting a new temp variable and test it
         var tmpName = Utils.GenerateIdentifier();
-        var tmp = new VariableStatement(tmpName, new NoTypeName(), new Identifier(leftId.Name), false);
+        var tmp = new VariableStatement(tmpName, NoTypeName.Instance, new Identifier(leftId.Name), false);
 
         var left = new BinaryOperatorExpression("=", new Identifier(leftId.Name), new Identifier(rightId.Name));
         var right = new BinaryOperatorExpression("=", new Identifier(rightId.Name), new Identifier(tmpName));