Consider replacing EventMachine with a more modern alternative

[mattheworiordan]

See https://github.com/ruby-concurrency/concurrent-ruby. It's an active project, where the community is headed, and has no additional dependencies!

EventMachine is arguably at EOL now, and issues in CI continue to plague this library: eventmachine/eventmachine#886

┆Issue is synchronized with this Jira Story by Unito

[kavalerov]

Additional option can be Ractor which is a part of Ruby 3.0 (https://ruby-doc.org/core-3.0.0/Ractor.html)

I am wondering if we can slightly change the title of this issue to something like "Consider replacing EventMachine with a more modern alternative", and then figuring out the right replacement will become a part of the issue.

[QuintinWillison]

Also see related internal Slack message and surrounding thread.

[lawrence-forooghian]

Whilst working on #396, it's become clear that EventMachine’s TLS handling leaves a lot to be desired. Another reason to consider moving away from it.