dqn: Fix poison vet check, use FsFile for logs, various cleanup

dqn_external.cpp

@@ -141,6 +141,10 @@ static STBSP__ASAN stbsp__uint32 stbsp__strlen_limited(char const *s, stbsp__uin
    return (stbsp__uint32)(sn - s);
 }
 
+
+#if defined(__clang__)
+ __attribute__((no_sanitize("undefined")))
+#endif
 STBSP__PUBLICDEF int STB_SPRINTF_DECORATE(vsprintfcb)(STBSP_SPRINTFCB *callback, void *user, char *buf, char const *fmt, va_list va)
 {
    static char hex[] = "0123456789abcdefxp";