Function build_config_sync_runtime 

pub fn build_config_sync_runtime(
    config: &ConfigSyncConfig,
    namespace: &str,
) -> Result<ConfigSyncRuntime>

Builds a namespaced config-sync runtime from static config.

This common backend factory owns backend dispatch, runtime ID generation, and transport-specific topic mapping. Product crates only pass their namespace and provide their reload callback to ConfigSyncRuntime::run_reload_subscription.