feat: add configuration loader for .env and JSON files

- Add ConfigLoader class for loading RateLimitConfig and GlobalConfig
- Support .env files with FASTAPI_TRAFFIC_* prefixed variables
- Support JSON configuration files with type validation
- Add convenience functions: load_rate_limit_config, load_global_config
- Add load_rate_limit_config_from_env, load_global_config_from_env
- Support custom environment variable prefixes
- Add comprehensive error handling with ConfigurationError
- Add 47 tests for configuration loading
- Add example 11_config_loader.py with 9 usage patterns
- Update examples/README.md with config loader documentation
- Update CHANGELOG.md with new feature
- Fix typo in limiter.py (errant 'fi' on line 4)

fastapi_traffic/core/limiter.py

@@ -22,7 +22,7 @@ logger = logging.getLogger(__name__)
 class RateLimiter:
     """Main rate limiter class that manages rate limiting logic."""
 
-    __slots__ = ("_config", "_backend", "_algorithms", "_initialized")
+    __slots__ = ("_algorithms", "_backend", "_config", "_initialized")
 
     def __init__(
         self,
@@ -96,15 +96,14 @@ class RateLimiter:
         identifier: str | None = None,
     ) -> str:
         """Build the rate limit key for a request."""
-        if identifier:
-            client_id = identifier
-        else:
-            client_id = config.key_extractor(request)
+        client_id = identifier or config.key_extractor(request)
 
         path = request.url.path
         method = request.method
 
-        return f"{self._config.key_prefix}:{config.key_prefix}:{method}:{path}:{client_id}"
+        return (
+            f"{self._config.key_prefix}:{config.key_prefix}:{method}:{path}:{client_id}"
+        )
 
     def _is_exempt(self, request: Request, config: RateLimitConfig) -> bool:
         """Check if the request is exempt from rate limiting."""
@@ -118,10 +117,7 @@ class RateLimiter:
         if client_ip in self._config.exempt_ips:
             return True
 
-        if request.url.path in self._config.exempt_paths:
-            return True
-
-        return False
+        return request.url.path in self._config.exempt_paths
 
     async def check(
         self,