- DCE: propagate parent methods to child classes so inherited proxy
  functions are generated (StringFlag.with_short etc.)
- stmt_codegen: return this.field.method() now checks field type
  (array/dict) instead of always assuming string
- stmt_codegen: fix missing f-prefix on two RET_VAR f-strings
- cli.ct: exit(0) after --help/--version to prevent double output
- Add TestInheritance tests covering all fixed bugs