* refactor: move tr_preallocation_mode info tr_open_files
* refactor: remove unnecessary error nullptr check
* refactor: use snake_case for private method names in inout.cc
* refactor: extract-method get_fd() from read_or_write_bytes()
* refactor: make function args const where possible
* refactor: simplify read_or_write_bytes()
* refactor: make buflen a uint64_t in read_or_write_piece()
* refactor: move tr_torrentStop() logic from read_or_write_piece() to tr_ioWrite()
* refactor: make tr_ioFoo() functions take a const torrent
* refactor: make tr_cache::close_torrent_files() take a tor_id instead of a torrent
