feat: added open timeout

[zhukaihan]

Summary

Adding open timeout.

module AmplitudeExperiment
  client = RemoteEvaluationClient.new("client-v0KqDA8KnJE4JHS3ZDaQTiwgjZENDMiR", RemoteEvaluationConfig.new(open_timeout_millis: 1, fetch_retries: 1, debug: true))
  client.fetch(User.new(user_id: "test_user", device_id: "test_device"))
end

Now causes:

D, [2025-04-06T23:23:10.319547 #3019] DEBUG -- : [Experiment] Fetching variants for user: {"device_id"=>"test_device", "user_id"=>"test_user"}
E, [2025-04-06T23:23:10.349484 #3019] ERROR -- : [Experiment] Fetch failed: execution expired
D, [2025-04-06T23:23:10.349530 #3019] DEBUG -- : [Experiment] Retrying fetch
E, [2025-04-06T23:23:10.854912 #3019] ERROR -- : [Experiment] Retry failed: execution expired
E, [2025-04-06T23:23:10.855015 #3019] ERROR -- : [Experiment] Retry Fetch failed: uncaught throw #<Net::OpenTimeout: execution expired>
E, [2025-04-06T23:23:10.855033 #3019] ERROR -- : [Experiment] Failed to fetch variants: execution expired

Checklist

• Does your PR title have the correct title format?
• Does your PR have a breaking change?: no

[Copilot]

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[github-actions]

🎉 This PR is included in version 1.6.0 🎉

The release is available on:

• v1.6.0
• GitHub release

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