common: Intentionally leak logger instance to fix hanging on Windows (#22273)

* Changed to leak logger singleton to prevent hanging on Windows

* Fix comment

* Stopped using static vector

Using std::vector will cause g_col to be released before the logger thread exits, causing the logger thread to touch freed memory causing a crash

* Change so all logs are output before exit

* Added debug logging

* added more logging

* Added logging

* Explicitly free logger to avoid hanging on Win

* Reverted to leak logger instance again

* Removed debug log and fixed comment

* Fixed comment

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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

common/log.h

@@ -49,7 +49,11 @@ void common_log_default_callback(enum ggml_log_level level, const char * text, v
 struct common_log;
 
 struct common_log * common_log_init();
-struct common_log * common_log_main(); // singleton, automatically destroys itself on exit
+
+// Singleton, intentionally leaked to avoid Windows teardown hangs.
+// Call common_log_flush() before exit if you want to ensure all logs are flushed.
+struct common_log * common_log_main();
+
 void                common_log_pause (struct common_log * log); // pause  the worker thread, not thread-safe
 void                common_log_resume(struct common_log * log); // resume the worker thread, not thread-safe
 void                common_log_free  (struct common_log * log);