feat(api-server): add Access-Control-Max-Age to CORS preflight responses (#3580)

Adds Access-Control-Max-Age: 600 to CORS preflight responses, telling
browsers to cache the preflight for 10 minutes. Reduces redundant OPTIONS
requests and improves perceived latency for browser-based API clients.

Salvaged from PR #3514 by aydnOktay.

Co-authored-by: aydnOktay <xaydinoktay@gmail.com>

gateway/platforms/api_server.py

@@ -307,6 +307,7 @@ class APIServerAdapter(BasePlatformAdapter):
         if "*" in self._cors_origins:
             headers = dict(_CORS_HEADERS)
             headers["Access-Control-Allow-Origin"] = "*"
+            headers["Access-Control-Max-Age"] = "600"
             return headers
 
         if origin not in self._cors_origins:
@@ -315,6 +316,7 @@ class APIServerAdapter(BasePlatformAdapter):
         headers = dict(_CORS_HEADERS)
         headers["Access-Control-Allow-Origin"] = origin
         headers["Vary"] = "Origin"
+        headers["Access-Control-Max-Age"] = "600"
         return headers
 
     def _origin_allowed(self, origin: str) -> bool: