feat: add hidden accessor for tag (#60)

Author: jackgerrits

src/main.cpp

@@ -998,7 +998,8 @@ PYBIND11_MODULE(_core, m)
                     [&](VW::cs_label* cs_label) { ex.l.cs = *cs_label; },
                 },
                 label);
-          });
+          })
+        .def("_get_tag", [](VW::example& ex) -> std::string { return std::string(ex.tag.data(), ex.tag.size()); });
 
   py::class_<workspace_with_logger_contexts>(m, "Workspace")
       .def(py::init(

src/vowpal_wabbit_next/_core.pyi

@@ -95,6 +95,7 @@ class DenseParameters():
 class Example():
     def __init__(self) -> None: ...
     def _get_label(self, arg0: LabelType) -> typing.Union[SimpleLabel, MulticlassLabel, CBLabel, CSLabel, None]: ...
+    def _get_tag(self) -> str: ...
     def _is_newline(self) -> bool: ...
     def _set_label(self, arg0: typing.Union[SimpleLabel, MulticlassLabel, CBLabel, CSLabel, None]) -> None: ...
     pass