[Rework] Add CFG_REF_* macros with debug logging for config refcounting

[Rework] Add CFG_REF_* macros with debug logging for config refcounting

Introduce specialized refcount macros for rspamd_config that provide
debug-level logging for better debugging of configuration lifecycle:

- CFG_REF_INIT_RETAIN: Initialize refcount to 1
- CFG_REF_RETAIN: Increment refcount
- CFG_REF_RELEASE: Decrement refcount and destroy if reaches 0

These macros use G_LOG_LEVEL_DEBUG to avoid cluttering info logs
with refcounting details, while still providing visibility when
debugging config lifetime issues.

Also update all workers and components to use the new CFG_REF_* macros
instead of generic REF_* macros for better tracking.