TalkAPI: added list_participants method + fix for statuses

[bigcat88]

While writing examples for documentation on how to work with the Talk API, I realized that there was no method for obtaining a list of participants in a conversation.
Now it is :)

A bug was also found that the statuses for one-to-one conversations were always empty.
Corrected and added a test for this.

[codecov]

Codecov Report

Merging #142 (dd987ef) into main (ddbd2c0) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #142   +/-   ##
=======================================
  Coverage   99.76%   99.76%           
=======================================
  Files          34       34           
  Lines        2926     2976   +50     
=======================================
+ Hits         2919     2969   +50     
  Misses          7        7           

Files	Coverage Δ
nc_py_api/_talk_api.py	100.00% <100.00%> (ø)
nc_py_api/talk.py	100.00% <100.00%> (ø)
nc_py_api/user_status.py	100.00% <100.00%> (ø)