Add missing list_sessions method

[Zsailer]

#22 introduced a bug by accidentally deleting the list_sessions method.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (main@7994444). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #26   +/-   ##
=======================================
  Coverage        ?   60.39%           
=======================================
  Files           ?        7           
  Lines           ?      356           
  Branches        ?       75           
=======================================
  Hits            ?      215           
  Misses          ?      124           
  Partials        ?       17           

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[blink1073]

Seems important. 😄