Gmail IMAP gets disconnected when moving an email to Trash #172

Description:
This issue was introduced around 2024 Q3 and is not specific to nmail, it can be reproduced with curl as well. It was reported in Google community forums - Gmail IMAP connection gets closed when moving an email to Trash - but it has not yet been fixed on Gmail side.

Since it's an inconvenience to have nmail lose server connection and reconnect every time one deletes email (with an Gmail account), the plan is to implement a workaround for Gmail using UID COPY to Trash, and then mark the email for deletion in source folder, and expunge emails marked for deletion.

How to reproduce it:
Set up nmail with a Gmail account, press d to delete an email.
The top right status message indicates Disconnected and then Reconnecting.

Environment:

• Version: v5.2.1
• OS / distro: macOS v15.1.1