✨ Add file state JSON export helpers

docs/README-en.md

@@ -191,6 +191,24 @@ if native_files_supported() {
 }
 ```
 
+File runtime state dump:
+
+```moonbit
+let logger = build_logger(
+  LoggerConfig::new(
+    sink=SinkConfig::new(kind=SinkKind::File, path="bitlogger-runtime.log"),
+    queue=Some(QueueConfig::new(16)),
+  ),
+)
+
+logger.info("queued hello")
+
+match logger.file_runtime_state() {
+  Some(snapshot) => println(stringify_runtime_file_state(snapshot, pretty=true))
+  None => ()
+}
+```
+
 ## Repository Layout
 
 - `bitlogger/`: MoonBit library package, tests, and Mooncake package README
@@ -215,6 +233,7 @@ if native_files_supported() {
 - `file_sink(...)` also supports `set_auto_flush(...)`, `set_rotation(...)`, and `clear_rotation()` for runtime policy updates.
 - `ConfiguredLogger` built through `build_logger(...)` also exposes `file_reopen()`, `file_reopen_with_current_policy()`, `file_reopen_append()`, `file_reopen_truncate()`, `file_flush()`, `file_close()`, `file_append_mode()`, `file_path()`, `file_auto_flush()`, `file_rotation_enabled()`, `file_rotation_config()`, `file_state()`, plus `file_set_append_mode(...)`, `file_set_auto_flush(...)`, `file_set_rotation(...)`, `file_clear_rotation()`, and the corresponding file failure counters, so config-driven file logging keeps a usable control surface.
 - `ConfiguredLogger` also exposes `file_runtime_state()` so queued file loggers can report both the underlying file snapshot and the outer queue backlog/drop state in one read.
+- `file_sink_state_to_json(...)`, `stringify_file_sink_state(...)`, `runtime_file_state_to_json(...)`, and `stringify_runtime_file_state(...)` can export file and queued-file snapshots directly as JSON for diagnostics or reporting.
 - `sink.text_formatter.template` currently supports fixed tokens: `{timestamp}`, `{timestamp_ms}`, `{level}`, `{target}`, `{message}`, and `{fields}`.
 - Config-driven sink assembly currently supports `console`, `json_console`, `text_console`, and `file`.
 - `queue` remains a synchronous bounded wrapper around the final sink, not an async runtime.