plugin: allow plugins to skip write of storage v.

Plugins may want to write several values at once and skip the first
writes to only save the values at the last call.

edmond/plugin.py

@@ -162,6 +162,7 @@ class Plugin:
         key: str,
         value: Any,
         ns: Optional[str] = None,
+        skip_save: bool = False,
     ) -> None:
         """Set a value in the plugin persistent storage."""
         name = ns or self.name
@@ -169,13 +170,15 @@ class Plugin:
             self.bot.storage[name] = {key: value}
         else:
             self.bot.storage[name][key] = value
-        self.bot.save_storage()
+        if not skip_save:
+            self.bot.save_storage()
 
     def append_storage_list_value(
         self,
         key: str,
         value: Any,
         ns: str = None,
+        skip_save: bool = False,
     ) -> None:
         """Append a value to a list in the plugin persistent storage."""
         name = ns or self.name
@@ -185,19 +188,22 @@ class Plugin:
             self.bot.storage[name][key] = [value]
         else:
             self.bot.storage[name][key].append(value)
-        self.bot.save_storage()
+        if not skip_save:
+            self.bot.save_storage()
 
     def remove_storage_list_value(
         self,
         key: str,
         value: Any,
         ns: Optional[str] = None,
+        skip_save: bool = False,
     ) -> None:
         """Remove a value from a persistent storage list."""
         name = ns or self.name
         if name in self.bot.storage and key in self.bot.storage[name]:
             self.bot.storage[name][key].remove(value)
-        self.bot.save_storage()
+        if not skip_save:
+            self.bot.save_storage()
 
     def should_read_message(self, message: str) -> Optional[str]:
         """Return a message content if it has been addressed to me, else None.