chore: replace any cast by asserting tool schema property types

Tightens the type assertion for the `unstableFilter` schema property in tests to ensure correct structural checking of its `type` and `description` fields.

packages/mcp-server/test/protocol.test.ts

@@ -72,7 +72,10 @@ describe("MCP protocol unstableFilter", () => {
       const tool = tools.find((t) => t.name === toolName);
       expect(tool).toBeDefined();
       expect(tool?.inputSchema.properties).toHaveProperty("unstableFilter");
-      const prop = tool?.inputSchema.properties.unstableFilter as any;
+      const prop = tool?.inputSchema.properties.unstableFilter as {
+        type: string;
+        description: string;
+      };
       expect(prop.type).toBe("boolean");
       expect(prop.description).toContain("optional");
       expect(prop.description).toContain("20%");