imapclient: Enhancement - Add custom interval to IDLE command

[birudeghi]

Although RFC states an IDLE timeout of 29 minutes, many IMAP servers timeout much earlier than that. Other forums point to around 10-13 minutes as a 'sweet spot'.

This PR gives more flexibility for those who need to adjust the restart interval. This also resolves issue #602

[emersion]

many IMAP servers timeout much earlier than that

Out of curiosity, do you have any examples of this?

Other forums point to around 10-13 minutes as a 'sweet spot'.

Any references?

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Generally I'd prefer for Idle to Do The Right Thing™ by default. In other words, if in practice a restart interval of 10 minutes works better, I'm not opposed to lowering the current timeout.

If there really is a need to allow the restart interval to be customized, I'd prefer to break the API and add an IdleOptions struct, rather than introduce a completely new function (which BTW is a copy-paste of the other one).

[birudeghi]

Lark IDLE timeout after every 10 minutes:

Your change (ca0ddb7) does its job, albeit having to implement reconnect logic ourselves