feat: allow *arg syntax with GroupedTable methods

this brings it in line with the normal Table methods

ibis/expr/types/groupby.py

@@ -63,15 +63,15 @@ def __getattr__(self, attr):
         else:
             return GroupedArray(field, self)
 
-    def aggregate(self, metrics=(), **kwds) -> ir.Table:
+    def aggregate(self, *metrics, **kwds) -> ir.Table:
         """Compute aggregates over a group by."""
         return self.table.to_expr().aggregate(
             metrics, by=self.groupings, having=self.havings, **kwds
         )
 
     agg = aggregate
 
-    def having(self, expr: ir.BooleanScalar) -> GroupedTable:
+    def having(self, *expr: ir.BooleanScalar) -> GroupedTable:
         """Add a post-aggregation result filter `expr`.
 
         ::: {.callout-warning}
@@ -92,7 +92,7 @@ def having(self, expr: ir.BooleanScalar) -> GroupedTable:
         havings = tuple(bind(table, expr))
         return self.copy(havings=self.havings + havings)
 
-    def order_by(self, expr: ir.Value | Iterable[ir.Value]) -> GroupedTable:
+    def order_by(self, *expr: ir.Value | Iterable[ir.Value]) -> GroupedTable:
         """Sort a grouped table expression by `expr`.
 
         Notes
@@ -261,7 +261,7 @@ def count(self) -> ir.Table:
             The aggregated table
         """
         table = self.table.to_expr()
-        return table.aggregate([table.count()], by=self.groupings, having=self.havings)
+        return table.aggregate(table.count(), by=self.groupings, having=self.havings)
 
     size = count