temporarily patch custom defined llm clients on api (#864)

# why
Serializing custom defined clients is not yet supported in the api

# what changed
If a custom LLM client is defined in the constructor, we log a warning
and disable api mode

# test plan

Author: miguelg719

.changeset/loud-ties-beg.md

@@ -0,0 +1,5 @@
+---
+"@browserbasehq/stagehand": patch
+---
+
+Temporarily patch custom clients serialization error on api

lib/index.ts

@@ -614,6 +614,13 @@ export class Stagehand {
 
     if (llmClient) {
       this.llmClient = llmClient;
+      this.logger({
+        category: "init",
+        message:
+          "Custom LLM clients are currently not supported in API mode",
+        level: 1,
+      });
+      this.usingAPI = false;
     } else {
       try {
         // try to set a default LLM client