style: unify code formatting and import order

- Remove trailing whitespace and normalize blank lines
- Unify string quotes and line breaks for long lines
- Sort imports alphabetically across modules

nanobot/providers/base.py

@@ -21,7 +21,7 @@ class LLMResponse:
     finish_reason: str = "stop"
     usage: dict[str, int] = field(default_factory=dict)
     reasoning_content: str | None = None  # Kimi, DeepSeek-R1 etc.
-    
+
     @property
     def has_tool_calls(self) -> bool:
         """Check if response contains tool calls."""
@@ -35,7 +35,7 @@ class LLMProvider(ABC):
     Implementations should handle the specifics of each provider's API
     while maintaining a consistent interface.
     """
-    
+
     def __init__(self, api_key: str | None = None, api_base: str | None = None):
         self.api_key = api_key
         self.api_base = api_base
@@ -79,7 +79,7 @@ class LLMProvider(ABC):
 
             result.append(msg)
         return result
-    
+
     @abstractmethod
     async def chat(
         self,
@@ -103,7 +103,7 @@ class LLMProvider(ABC):
             LLMResponse with content and/or tool calls.
         """
         pass
-    
+
     @abstractmethod
     def get_default_model(self) -> str:
         """Get the default model for this provider."""