fix: Support 'args' key in response tool call argument extraction

Some frameworks (e.g. LangGraph Python) return tool calls with an
'args' key instead of 'arguments'. Add 'args' as a fallback in
checkResponseToolCalls so these tool calls are validated correctly.

Refs PY-2281
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ericapisani

src/test-cases/checks.ts

@@ -875,6 +875,7 @@ export function checkResponseToolCalls(
         let actualArgs: Record<string, unknown>;
         const argsRaw =
           foundCall.arguments ||
+          foundCall.args ||
           (foundCall.function as Record<string, unknown>)?.arguments;
 
         if (typeof argsRaw === "string") {