Updating ld-eventsource and yggdrasil-engine dependencies which require minimal Ruby version 3.1

[rgisiger]

About the changes

I updated ld-eventsource which was pinned to a fixed version. This change brings a minimal required version of Ruby 3.1.

I took the chance to update as well yggdrasil-engine to the latest version which was released recently.

All tests were green for rspec and rubocop.

Discussion points

I suggest to bump version of Unleash to version 7 since it brings a breaking change for the Ruby version.

[gee-forr]

@rgisiger - thanks for this!!! I was wondering if you could specify ~> 2.5 for ld-eventsource instead of ~> 2.5.1.

Reason for this is that 2.5.1 requires http at >= 4.4.1, < 6.0.0, whereas 2.6.0 which was recently released has changed its http version req to >= 4.4.1, < 7.0.0.

We're currently blocked from upgrading http from 5.x to 6 because of unleash's transitive dep on ld-eventsource. Your changes as they stand now will still prevent an upgrade of http.