fix(lint): Remove trailing whitespace and add ClassVar annotations to PureGraph benchmarks

- Fix RUF012: Annotate mutable class attributes (params, param_names) with
  typing.ClassVar in PureGraphBench benchmark suite
- Fix W293: Remove trailing whitespace from blank lines in benchmark file

This fixes the CI lint check that was failing on the pr-creator generated
benchmark code.

ISSUES CLOSED: #9531

benchmarks/pure_graph_bench.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from typing import Any
+from typing import Any, ClassVar
 
 from cleveragents.langgraph.nodes import Edge, NodeConfig, NodeType
 from cleveragents.langgraph.pure_graph import PureGraph
@@ -11,8 +11,8 @@ from cleveragents.langgraph.pure_graph import PureGraph
 class PureGraphBench:
     """Benchmark suite for PureGraph execution performance."""
 
-    params = [10, 50, 100, 500]
-    param_names = ["node_count"]
+    params: ClassVar[list[int]] = [10, 50, 100, 500]
+    param_names: ClassVar[list[str]] = ["node_count"]
 
     def setup(self, node_count: int) -> None:
         """Set up benchmark with varying node counts."""
@@ -22,7 +22,7 @@ class PureGraphBench:
             "end": NodeConfig(name="end", type=NodeType.END),
         }
         self.edges: list[Edge] = []
-        
+
         # Create a linear chain of nodes
         previous = "start"
         for i in range(node_count):
@@ -34,14 +34,14 @@ class PureGraphBench:
             )
             self.edges.append(Edge(source=previous, target=node_name))
             previous = node_name
-        
+
         self.edges.append(Edge(source=previous, target="end"))
-        
+
         # Create function registry with identity functions
         self.fn_registry: dict[str, Any] = {
             f"fn_{i}": lambda x, i=i: x for i in range(node_count)
         }
-        
+
         self.graph = PureGraph(
             name=f"bench_graph_{node_count}",
             nodes=self.nodes,