Improve stream and decryption performance in the chat

[MaxDac]

Implement the chat using the streams available in Phoenix LiveView. Useful links:

• Example using streams.
• Building a chat example.
• Documentation.

[MaxDac]

Edit: the streams usage have been implemented in #88, but their implementation still relies on the usage of the complete message list, which would remain in memory for the LiveView socket GenServer. Possible solution:

• Instead of saving the whole chat list, save only the last message and pass it in input to the function that compute the additional properties of the message being sent.

Chat decryption

Improve the chat decryption performance, as now every time a new chat has to be decrypted, the private key must be taken from the IndexedDB.

[MaxDac]

Reopening this to increase the performance of the chat parsing at the beginning of the chat LIveView mounting, while creating the Stream.

[MaxDac]

Reopening the issue to improve the performance of the chat mounting, when all the chat entries are processed.
The algorithm should act on adding a maximum chats to load, and then lazy loading the older chats (if existent).