chore(runtime): remove dead StreamSessionEventsWithRetry + orphaned connection events

[aheritier]

Summary

pkg/runtime/client.go:730-797 StreamSessionEventsWithRetry has broken retry semantics AND zero callers of any kind (verified repo-wide). Its ConnectionLost/ConnectionRestored events also have no other producer and no consumer anywhere.

Fix

Delete StreamSessionEventsWithRetry, the orphaned ConnectionLost/ConnectionRestored events, and their decoder/registration. Re-verify with a repo-wide grep in the PR that nothing references them.

Acceptance

• Code removed; build + tests green; grep confirms no references remain.