Fix: Fix streaming response body type checking for Node.js compatibility (#292)

The 'in' operator fails when response.body is not a plain object (e.g., ReadableStream in Node.js).
Added proper type checking before using the 'in' operator to prevent runtime errors.

This resolves issues with streaming responses that contain ReadableStream bodies instead of plain objects.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <[email protected]>

Author: xavidop

src/github_llms.ts

@@ -1202,21 +1202,21 @@ export function githubModel(
       }
       return {
         message:
-          "choices" in response.body
+          (typeof response.body === 'object' && response.body && "choices" in response.body)
             ? fromGithubChoice(
                 response.body.choices[0],
                 request.output?.format === "json",
               ).message
             : { role: "model", content: [] },
         usage: {
           inputTokens:
-            "usage" in response.body ? response.body.usage?.prompt_tokens : 0,
+            (typeof response.body === 'object' && response.body && "usage" in response.body) ? response.body.usage?.prompt_tokens : 0,
           outputTokens:
-            "usage" in response.body
+            (typeof response.body === 'object' && response.body && "usage" in response.body)
               ? response.body.usage?.completion_tokens
               : 0,
           totalTokens:
-            "usage" in response.body ? response.body.usage?.total_tokens : 0,
+            (typeof response.body === 'object' && response.body && "usage" in response.body) ? response.body.usage?.total_tokens : 0,
         },
         custom: response,
       };