fix(io): add read_parquet and read_csv to base backend mixin

xref #5420

This adds `read_parquet` and `read_csv` as methods to the
`FileIOHandler` mixin (renamed from `ResultHandler`).

Now every backend will have these two `read_` methods and will raise a
`NotImplementedError`.

Co-authored-by: Olivier Grisel <olivier.grisel@ensta.org>

ibis/backends/base/__init__.py

@@ -214,8 +214,7 @@ def _ipython_key_completions_(self) -> list[str]:
         return self._backend.list_tables()
 
 
-# should have a better name
-class ResultHandler:
+class _FileIOHandler:
     @staticmethod
     def _import_pyarrow():
         try:
@@ -322,8 +321,56 @@ def to_pyarrow_batches(
         """
         raise NotImplementedError
 
+    def read_parquet(
+        self, path: str | Path, table_name: str | None = None, **kwargs: Any
+    ) -> ir.Table:
+        """Register a parquet file as a table in the current backend.
 
-class BaseBackend(abc.ABC, ResultHandler):
+        Parameters
+        ----------
+        path
+            The data source.
+        table_name
+            An optional name to use for the created table. This defaults to
+            a sequentially generated name.
+        **kwargs
+            Additional keyword arguments passed to the backend loading function.
+
+        Returns
+        -------
+        ir.Table
+            The just-registered table
+        """
+        raise NotImplementedError(
+            f"{self.name} does not support direct registration of parquet data."
+        )
+
+    def read_csv(
+        self, path: str | Path, table_name: str | None = None, **kwargs: Any
+    ) -> ir.Table:
+        """Register a CSV file as a table in the current backend.
+
+        Parameters
+        ----------
+        path
+            The data source. A string or Path to the CSV file.
+        table_name
+            An optional name to use for the created table. This defaults to
+            a sequentially generated name.
+        **kwargs
+            Additional keyword arguments passed to the backend loading function.
+
+        Returns
+        -------
+        ir.Table
+            The just-registered table
+        """
+        raise NotImplementedError(
+            f"{self.name} does not support direct registration of CSV data."
+        )
+
+
+class BaseBackend(abc.ABC, _FileIOHandler):
     """Base backend class.
 
     All Ibis backends must subclass this class and implement all the