feat: add ObjBlock type, block compilation, and newline skipping in parser

Introduce a new ObjBlock object type with OBJ_BLOCK tag, replacing the placeholder OBJ_NUM in makeBlock(). Refactor the compiler to separate Parser and Compiler structs, adding skipNewlines and hasError fields to Parser and a parent pointer to Compiler for nested block support. Implement compileBlock() function that compiles a block up to a specified end token, and update callBlock() in the VM to push empty slots for local variables. Adjust token reading functions to accept Parser instead of Compiler, and remove the MAX_TOKEN enum entry.

example/hello.wren

@@ -1,4 +1,6 @@
-class Foo {}
+{
+  123
+}
 var a = 123
 var b = 345
 a