Logger simplification (#883)

- **`Logger` now holds a single `SinkPtr`** instead of a `std::vector<SinkPtr>`. The `SetSinks`/`AddSink` API is replaced with a single `SetSink`. This removes complexity from `Logger` itself and makes `Clone()` cheaper (no vector copy).

- **New `BroadcastSink`** (`zencore/logging/broadcastsink.h`) acts as a thread-safe, shared indirection point that fans out to a dynamic list of child sinks. Adding or removing a child sink via `AddSink`/`RemoveSink` is immediately visible to every `Logger` that holds a reference to it — including cloned loggers — without requiring each logger to be updated individually.

- **`GetDefaultBroadcastSink()`** (exposed from `zenutil/logging.h`) gives server-layer code access to the shared broadcast sink so it can register optional sinks (OTel, TCP log stream) after logging is initialized, without going through `Default()->AddSink()`.

### Motivation

Previously, dynamically adding sinks post-initialization mutated the default logger's internal sink vector directly. This was fragile: cloned loggers (created before `AddSink` was called) would not pick up the new sinks. `BroadcastSink` fixes this by making the sink list a shared, mutable object that all loggers sharing the same broadcast instance observe uniformly.

0 files changed, 0 insertions, 0 deletions