fix: use correct boto3 service name for evaluation client (#267)

Change 'agentcore-evaluation-dataplane' to 'bedrock-agentcore' in
StrandsEvalsAgentCoreEvaluator, fixing UnknownServiceError on init.

Closes #266

Author: jariy17

src/bedrock_agentcore/evaluation/integrations/strands_agents_evals/evaluator.py

@@ -98,7 +98,7 @@ def __init__(
 
         # Create client with provided or default config
         client_config = config or self._get_default_config()
-        self.client = boto3.client("agentcore-evaluation-dataplane", region_name=region, config=client_config)
+        self.client = boto3.client("bedrock-agentcore", region_name=region, config=client_config)
 
     @staticmethod
     def _get_default_config() -> Config: