✨ Add config JSON export helpers

docs/README-en.md

@@ -222,6 +222,7 @@ match logger.file_runtime_state() {
 ## Config Notes
 
 - BitLogger now includes a JSON config layer via `parse_logger_config_text(...)`, `stringify_logger_config(...)`, and `build_logger(...)`.
+- `QueueConfig`, `TextFormatterConfig`, and `SinkConfig` can also be exported independently through `queue_config_to_json(...)` / `stringify_queue_config(...)`, `text_formatter_config_to_json(...)` / `stringify_text_formatter_config(...)`, and `sink_config_to_json(...)` / `stringify_sink_config(...)`.
 - Supported keys include `min_level`, `target`, `timestamp`, `sink.kind`, `sink.path`, `sink.append`, `sink.auto_flush`, `sink.rotation`, `sink.text_formatter`, and `queue`.
 - `sink.rotation` currently supports `max_bytes` and `max_backups` for basic size-based rotation and backup retention.
 - `file_sink(...)` also exposes `reopen()`, `reopen_with_current_policy()`, `reopen_append()`, `reopen_truncate()`, `open_failures()`, `write_failures()`, `flush_failures()`, and `rotation_failures()` for basic observability.

docs/changes/0.3.0.md

@@ -11,6 +11,7 @@ version 0.3.0
 - feat: add `TextFormatterConfig::to_formatter()` for bridging parsed config into runtime formatter setup
 - feat: add `parse_logger_config_text(...)` for JSON config parsing
 - feat: add `logger_config_to_json(...)` and `stringify_logger_config(...)` for config serialization
+- feat: add standalone JSON export helpers for `QueueConfig`, `TextFormatterConfig`, and `SinkConfig`
 - feat: add `RuntimeSink`, `ConfiguredLogger`, `build_logger(...)`, and `parse_and_build_logger(...)` for config-driven logger assembly
 - feat: add `ConfiguredLogger::drain(...)`, `ConfiguredLogger::pending_count()`, and `ConfiguredLogger::dropped_count()` queue observability helpers
 - feat: add `bitlogger_async/` as a separate native-target async adapter package
@@ -56,6 +57,7 @@ version 0.3.0
 - test: cover parsing of core logger config fields
 - test: cover nested formatter and queue config parsing
 - test: cover config stringify and parse roundtrip behavior
+- test: cover stable JSON export for reusable config subtypes
 - test: cover config-built queued text logger flushing and pending count behavior
 - test: cover partial drain behavior for config-built queued logger
 - test: cover dropped-count reporting for bounded config-built queue
@@ -82,6 +84,7 @@ version 0.3.0
 - docs: add `examples/async_basic` to show async worker startup and queue-backed logging flow
 - docs: update `examples/async_basic` to use unified JSON-driven async logger config
 - docs: update root README, English README, and Mooncake README with config usage notes
+- docs: document standalone JSON export helpers for reusable config subtypes
 - docs: update formatter examples to demonstrate template-based text rendering
 - docs: update file sink examples to demonstrate rotation and backup retention
 - docs: document file sink reopen and observability counters in README variants