$each modifier is not handled correctly in $addToSet command

[sumezulike]

Using the $each modifier with $addToSet doesn't always result in unique values because of how the values of the $each are handled:

https://github.com/mongomock/mongomock/blob/ca41f27161c50d83d5ef8c899623084dd6f09a1d/mongomock/collection.py#LL704C37-L706C80

Example:

import mongomock

client = mongomock.MongoClient()
coll = client.db.coll
id = coll.insert_one({"numbers": []}).inserted_id

coll.find_one_and_update({"_id": id}, {"$addToSet": {"numbers": {"$each": [1, 1, 1, 1]}}})
print(coll.find_one({"_id": id}))

This will result in {"numbers": [1, 1, 1, 1]} instead of {"numbers": [1]}.