We add log4rs create for logging across Zellij. Additionally, we capture
`stderr` output from plugins and log it the same log file as other
Zellij logs.
* refactor(os_input_output): use Pid for child process
* fix(debug): change debug_to_file to write &[u8]
This patch changes debug_to_file to write entire slices in one call, to
avoid the overhead of opening and closing files for each byte written.
* refactor(ServerOsApi): remove unnecessary muts from methods
Co-authored-by: KOVACS Tamas <ktamas@fastmail.fm>
