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

Cargo.toml

@@ -7,7 +7,7 @@ edition = "2024"
 crate-type = ["cdylib"]
 
 [dependencies]
-ngx = "0.4.1"
+ngx = "0.5.0"
 rusqlite = "0.37.0"
 handlebars = "6.3.2"
 serde = { version = "1.0", features = ["derive"] }