feat(expr-ir): The big Selector overhaul

.pre-commit-config.yaml

@@ -106,7 +106,8 @@ repos:
             narwhals/.*typing\.py|
             narwhals/_plan/functions\.py|
             narwhals/_plan/expressions/ranges\.py|
-            narwhals/_plan/schema\.py
+            narwhals/_plan/schema\.py|
+            narwhals/_plan/expressions/selectors\.py
           )
     - id: pull-request-target
       name: don't use `pull_request_target`

narwhals/_plan/__init__.py

@@ -1,8 +1,8 @@
 from __future__ import annotations
 
+from narwhals._plan import selectors
 from narwhals._plan.dataframe import DataFrame
-from narwhals._plan.expr import Expr, Selector
-from narwhals._plan.expressions import selectors
+from narwhals._plan.expr import Expr
 from narwhals._plan.functions import (
     all,
     all_horizontal,
@@ -25,6 +25,7 @@
     sum_horizontal,
     when,
 )
+from narwhals._plan.selectors import Selector
 from narwhals._plan.series import Series
 
 __all__ = [