Initial commit: fastapi-traffic rate limiting library

- Core rate limiting with multiple algorithms (sliding window, token bucket, etc.)
- SQLite and memory backends
- Decorator and dependency injection patterns
- Middleware support
- Example usage files

fastapi_traffic/backends/base.py

@@ -0,0 +1,89 @@
+"""Abstract base class for rate limit storage backends."""
+
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import Any
+
+
+class Backend(ABC):
+    """Abstract base class for rate limit storage backends."""
+
+    @abstractmethod
+    async def get(self, key: str) -> dict[str, Any] | None:
+        """Get the current state for a key.
+
+        Args:
+            key: The rate limit key.
+
+        Returns:
+            The stored state dictionary or None if not found.
+        """
+        ...
+
+    @abstractmethod
+    async def set(self, key: str, value: dict[str, Any], *, ttl: float) -> None:
+        """Set the state for a key with TTL.
+
+        Args:
+            key: The rate limit key.
+            value: The state dictionary to store.
+            ttl: Time-to-live in seconds.
+        """
+        ...
+
+    @abstractmethod
+    async def delete(self, key: str) -> None:
+        """Delete the state for a key.
+
+        Args:
+            key: The rate limit key.
+        """
+        ...
+
+    @abstractmethod
+    async def exists(self, key: str) -> bool:
+        """Check if a key exists.
+
+        Args:
+            key: The rate limit key.
+
+        Returns:
+            True if the key exists, False otherwise.
+        """
+        ...
+
+    @abstractmethod
+    async def increment(self, key: str, amount: int = 1) -> int:
+        """Atomically increment a counter.
+
+        Args:
+            key: The rate limit key.
+            amount: The amount to increment by.
+
+        Returns:
+            The new value after incrementing.
+        """
+        ...
+
+    @abstractmethod
+    async def clear(self) -> None:
+        """Clear all rate limit data."""
+        ...
+
+    async def close(self) -> None:
+        """Close the backend connection."""
+        pass
+
+    async def __aenter__(self) -> Backend:
+        """Async context manager entry."""
+        return self
+
+    async def __aexit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: Any,
+    ) -> None:
+        """Async context manager exit."""
+        await self.close()