possible leaks in add_file function

There is no fclose after fopen for file variable.

```
fflush(file);
//fclose(file)<===missing!!
VLOG_F(g_internal_verbosity, "Logging to '" LOGURU_FMT(s) "', mode: '" LOGURU_FMT(s) "', verbosity: " LOGURU_FMT(d) "", path, mode_str, verbosity);
return true;
```

Search the repository for the add_file function and inspect the fopen, fflush, and return path shown in the issue. Verify the file-resource lifecycle and check existing tests or build instructions for log-file handling. Done means the reported leak is addressed and the project still builds and its relevant tests pass.

Written by the indexing model from the issue text.