roster: extract to a separate module

pqcli/__main__.py

@@ -1,25 +1,20 @@
-import pickle
 from pathlib import Path
 
 import xdg
 
-from pqcli.mechanic import Roster
+from pqcli.roster import Roster
 from pqcli.ui import Ui
 
 SAVE_PATH = Path(xdg.XDG_CONFIG_HOME) / "pqcli" / "save.dat"
 
 
 def main() -> None:
-    if SAVE_PATH.exists():
-        roster = pickle.loads(SAVE_PATH.read_bytes())
-    else:
-        roster = Roster()
+    roster = Roster.load(SAVE_PATH)
 
     try:
         Ui(roster).run()
     finally:
-        SAVE_PATH.parent.mkdir(parents=True, exist_ok=True)
-        SAVE_PATH.write_bytes(pickle.dumps(roster))
+        roster.save(SAVE_PATH)
 
 
 if __name__ == "__main__":