Disable debug logging in release builds #420

Tracking the TODO in packages/host/cpp/Logger.cpp.

log_debug formats and emits unconditionally — there is no build-configuration guard anywhere in Logger.cpp. The host calls it on every addon load: per-library "Found napi_register_module_v1", per-library "Failed to find…", and the resolution chatter in CxxNodeApiHostModule.cpp. In a shipped app that is per-addon logging to logcat / os_log that no user asked for, plus the string formatting cost on a path that runs during startup.

Two things to decide:

1. What "release" means here. NDEBUG is the obvious hook and is set by the CMake Release/MinSizeRel configurations, but RelWithDebInfo also defines it — which may or may not be what we want given Support RelWithDebInfo in CMake RN #255. React Native's own NDEBUG/__DEV__ split is worth mirroring rather than inventing something.
2. Compile out vs. gate at runtime. Compiling the body away removes the formatting cost entirely; a runtime level check keeps the ability to turn logging on when diagnosing a release-only problem — which, given that release-mode issues are the hard ones, has real value. A compile-time default with a runtime override is the usual compromise.

log_warning and log_error should keep firing in release regardless.

Also a prerequisite for making release-mode CI runs readable — see the iOS Release-mode CI issue.