fix: Declare logger as a runtime dependency

[jsonbailey]

Problem

On Ruby 4.0, require "ld-eventsource" fails with:

cannot load such file -- logger (LoadError)

This happens in any app that does not already pull in the logger gem.

Cause

lib/ld-eventsource/client.rb requires logger, but the gemspec lists logger only as a development dependency. Ruby 4.0 removed logger from the default gems, so it is not available unless something declares it.

Fix

Move logger from add_development_dependency to add_runtime_dependency. The constraint stays ~> 1.5. Ruby 3.1 (the oldest supported version) ships logger 1.5.0, so this does not force an upgrade there.

Proof

A Bundler project with only gem "ld-eventsource", path: <this branch>, on Ruby 4.0.6, running bundle exec ruby -e 'require "ld-eventsource"; puts :ok':

• Before: cannot load such file -- logger (LoadError)
• After: ok (Bundler resolves logger 1.7.0)

Other requires checked

All require calls in lib/. Standard-library ones are logger, thread, and uri. thread is built in and uri is still a default gem in Ruby 4.0, so only logger needs a change. The code does not use base64, ostruct, cgi, bigdecimal, or json directly (JSON bodies go through the http gem).

Tests

• bundle exec rspec spec: 174 examples, 0 failures
• bundle exec rubocop --parallel: 16 files inspected, no offenses

CI covers Ruby 3.2, 3.3, 3.4, JRuby 9.4 and JRuby 10.0. It does not include Ruby 4.0.

Impact

The Ruby server SDK is not affected, because its lock file pulls in logger through other gems.

Jira: SDK-3207

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Note

Overview
Fixes LoadError when requiring ld-eventsource on Ruby 4.0, where logger is no longer a default gem even though lib/ld-eventsource/client.rb requires it.

The gemspec now declares logger (~> 1.5) as a runtime dependency instead of a development-only dependency, so Bundler installs it for consumers. The version constraint is unchanged and remains compatible with Ruby 3.1’s bundled logger.

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