chore: performance improvement for resample. (#1042)

Author: Genesis929

bigframes/core/compile/compiler.py

@@ -147,8 +147,8 @@ def compile_fromrange(self, node: nodes.FromRangeNode, ordered: bool = True):
         ).name("labels")
         labels = (
             typing.cast(ibis.expr.types.ArrayValue, labels_array_table)
-            .unnest()
             .as_table()
+            .unnest(["labels"])
         )
         if ordered:
             return compiled.OrderedIR(