Fix ngx 0.5.0 API compatibility

- Update HttpModule trait implementation to match ngx 0.5.0 API
- Implement HttpModuleLocationConf as separate unsafe trait
- Fix configuration access using Module::location_conf()
- Replace ngx_null_command macro with explicit null command
- Update imports to use correct constant names
- Suppress C FFI naming convention warnings

.cursorrules

@@ -0,0 +1 @@
+- Always use `direnv exec "$PWD"` when invoking cargo and other tools that need access to the nix/direnv environment