fix(strands-memory): restore positional arg order in AgentCoreMemorySessionManager.__init__

PR #288 inserted `converter` as the 2nd positional parameter, shifting
`region_name` from position 2 to 3. Any caller passing region_name
positionally (e.g. `AgentCoreMemorySessionManager(config, REGION)`)
silently assigned the region string to `converter`, leaving
region_name=None and causing botocore.exceptions.NoRegionError.

Move `converter` after the existing positional params and make it
keyword-only (after `*`) to restore backward compatibility and prevent
future positional misuse.

Author: tejaskash

src/bedrock_agentcore/memory/integrations/strands/session_manager.py

@@ -104,22 +104,23 @@ def _get_monotonic_timestamp(cls, desired_timestamp: Optional[datetime] = None)
     def __init__(
         self,
         agentcore_memory_config: AgentCoreMemoryConfig,
-        converter: Optional[type[MemoryConverter]] = None,
         region_name: Optional[str] = None,
         boto_session: Optional[boto3.Session] = None,
         boto_client_config: Optional[BotocoreConfig] = None,
+        *,
+        converter: Optional[type[MemoryConverter]] = None,
         **kwargs: Any,
     ):
         """Initialize AgentCoreMemorySessionManager with Bedrock AgentCore Memory.
 
         Args:
             agentcore_memory_config (AgentCoreMemoryConfig): Configuration for AgentCore Memory integration.
-            converter (Optional[type[MemoryConverter]], optional): Optional custom converter.
-                If None, native Bedrock/Strands converter is used.
             region_name (Optional[str], optional): AWS region for Bedrock AgentCore Memory. Defaults to None.
             boto_session (Optional[boto3.Session], optional): Optional boto3 session. Defaults to None.
             boto_client_config (Optional[BotocoreConfig], optional): Optional boto3 client configuration.
                Defaults to None.
+            converter (Optional[type[MemoryConverter]], optional): Optional custom converter.
+                If None, native Bedrock/Strands converter is used.
             **kwargs (Any): Additional keyword arguments.
         """
         self.converter = converter or AgentCoreMemoryConverter