fix: resolve local names in methods as self sends instead of upvalues

When a method references a name that exists as a local variable outside the method boundary, the compiler now correctly treats it as a self send rather than closing over the outer local. This fixes the closure resolution logic in `findUpvalue` to stop searching for upvalues when hitting a method boundary, unless the name starts with '_' indicating a static field access. The change removes two incorrect test cases that expected outer local closure behavior and adds a new test verifying that both instance and static methods resolve local names to their own methods.

test/language/variable/local_outside_method.wren

@@ -0,0 +1,22 @@
+{
+  var foo = "variable"
+
+  class Foo {
+    construct new() {}
+
+    foo { "method" }
+
+    method {
+      System.print(foo)
+    }
+
+    static foo { "class method" }
+
+    static classMethod {
+      System.print(foo)
+    }
+  }
+
+  Foo.new().method // expect: method
+  Foo.classMethod  // expect: class method
+}