fix: address code review issues in LLM and RAG protocols

- Fix ModelNotAvailableError to properly pass provider/model to base exception
- Fix RateLimitError type annotation (Optional[str] instead of str = None)
- Fix ContextLengthExceededError to accept and pass provider/model parameters
- Add async aretrieve method to RetrievalStrategyProtocol for async I/O support
- Add missing newline at end of protocols.py file

Addresses review feedback from code reviewers.

Co-authored-by: Mervin Praison <MervinPraison@users.noreply.github.com>

Author: MervinPraison

src/praisonai-agents/praisonaiagents/llm/protocols.py

@@ -233,23 +233,23 @@ def __init__(self, message: str, provider: Optional[str] = None, model: Optional
 class RateLimitError(LLMProviderError):
     """Raised when rate limit is exceeded."""
 
-    def __init__(self, message: str = None, retry_after: Optional[float] = None):
+    def __init__(self, message: Optional[str] = None, retry_after: Optional[float] = None, provider: Optional[str] = None, model: Optional[str] = None):
         self.retry_after = retry_after
-        super().__init__(message or "Rate limit exceeded")
+        super().__init__(message or "Rate limit exceeded", provider=provider, model=model)
 
 
 class ModelNotAvailableError(LLMProviderError):
     """Raised when requested model is not available."""
 
     def __init__(self, model: str, provider: Optional[str] = None):
-        self.model = model
-        super().__init__(f"Model '{model}' is not available{f' from provider {provider}' if provider else ''}")
+        message = f"Model '{model}' is not available{f' from provider {provider}' if provider else ''}"
+        super().__init__(message, provider=provider, model=model)
 
 
 class ContextLengthExceededError(LLMProviderError):
     """Raised when input exceeds model's context length."""
 
-    def __init__(self, tokens: int, max_tokens: int):
+    def __init__(self, tokens: int, max_tokens: int, provider: Optional[str] = None, model: Optional[str] = None):
         self.tokens = tokens
         self.max_tokens = max_tokens
-        super().__init__(f"Input length ({tokens} tokens) exceeds model limit ({max_tokens} tokens)")
+        super().__init__(f"Input length ({tokens} tokens) exceeds model limit ({max_tokens} tokens)", provider=provider, model=model)

src/praisonai-agents/praisonaiagents/rag/protocols.py

@@ -153,6 +153,30 @@ def retrieve(
             List of retrieved documents with metadata
         """
         ...
+    
+    async def aretrieve(
+        self,
+        query: str,
+        knowledge_store: Any,  # KnowledgeStoreProtocol
+        *,
+        limit: int = 10,
+        filters: Optional[Dict[str, Any]] = None,
+        **kwargs: Any,
+    ) -> List[Dict[str, Any]]:
+        """
+        Async version of retrieve.
+        
+        Args:
+            query: Search query string
+            knowledge_store: Knowledge store to search
+            limit: Maximum number of results
+            filters: Optional metadata filters
+            **kwargs: Strategy-specific options
+            
+        Returns:
+            List of retrieved documents with metadata
+        """
+        ...
 
 
 @runtime_checkable