fix: remove default constructors and require explicit construct new() for all user classes

The compiler no longer auto-generates a default `new()` constructor for classes. All classes must now explicitly define `construct new() {}` to be instantiable. This change removes the `createDefaultConstructor` function from the compiler, eliminates the `return_this` primitive used by Object's default initializer, and adds explicit constructors to all test and example classes. Core metaclasses (Bool, Class, Null, Num, Object, Range, Sequence) now correctly reject `new()` calls with runtime errors.

test/language/method/arity.wren

@@ -1,4 +1,5 @@
 class Foo {
+  construct new() {}
   method { "getter" }
   method() { "no args" }
   method(a) { a }

test/language/method/empty_block.wren

@@ -1,4 +1,5 @@
 class Foo {
+  construct new() {}
   bar {}
 }
 

test/language/method/long_name.wren

@@ -1,4 +1,5 @@
 class Foo {
+  construct new() {}
   thisHasAMethodNameThatIsExactly64CharactersLongWhichIsTheMaximum {
     return "result"
   }

test/language/method/many_methods.wren

@@ -1,4 +1,5 @@
 class Foo {
+  construct new() {}
   method000 { 1 }
   method001 { 1 }
   method002 { 1 }

test/language/method/newlines.wren

@@ -1,4 +1,5 @@
 class Foo {
+  construct new() {}
   method(a, b) { "method " + a + " " + b }
   [a, b] { "subscript " + a + " " + b }
 }

test/language/method/not_found.wren

@@ -1,3 +1,5 @@
-class Foo {}
+class Foo {
+  construct new() {}
+}
 
 Foo.new().someUnknownMethod // expect runtime error: Foo does not implement 'someUnknownMethod'.

test/language/method/not_found_eleven_arguments.wren

@@ -1,3 +1,5 @@
-class Foo {}
+class Foo {
+  construct new() {}
+}
 
 Foo.new().someUnknownMethod(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) // expect runtime error: Foo does not implement 'someUnknownMethod(_,_,_,_,_,_,_,_,_,_,_)'.

test/language/method/not_found_multiple_arguments.wren

@@ -1,3 +1,5 @@
-class Foo {}
+class Foo {
+  construct new() {}
+}
 
 Foo.new().someUnknownMethod(1, 2) // expect runtime error: Foo does not implement 'someUnknownMethod(_,_)'.

test/language/method/not_found_one_argument.wren

@@ -1,3 +1,5 @@
-class Foo {}
+class Foo {
+  construct new() {}
+}
 
 Foo.new().someUnknownMethod(1) // expect runtime error: Foo does not implement 'someUnknownMethod(_)'.

test/language/method/operators.wren

@@ -1,4 +1,6 @@
 class Foo {
+  construct new() {}
+
   +(other) { "infix + " + other }
   -(other) { "infix - " + other }
   *(other) { "infix * " + other }

test/language/method/static.wren

@@ -1,4 +1,5 @@
 class Foo {
+  construct new() {}
   bar { "on instance" }
   static bar { "on metaclass" }
 

test/language/method/subscript_operators.wren

@@ -1,4 +1,5 @@
 class Foo {
+  construct new() {}
   [a] { "1-subscript " + a }
   [a, b] { "2-subscript " + a + " " + b }
   [a, b, c] { "3-subscript " + a + " " + b + " " + c }