feat: add Sequence.all method and forall documentation with tests

Implement `all(f)` method on Sequence class that returns true if all elements pass the predicate function. Add corresponding documentation entry for `forall(predicate)` in core-library.markdown. Include three test files covering basic functionality, non-boolean return handling, and non-function argument error cases.

builtin/core.wren

@@ -14,6 +14,13 @@ class Sequence {
     }
     return result
   }
+
+  all(f) {
+    for (element in this) {
+      if (!f.call(element)) return false
+    }
+    return true
+  }
 }
 
 class List is Sequence {