chore(release): version 1.28.0 (#1480)

chore: remove experiment around say_stream (#1471)

chore(deps): bump dependabot/fetch-metadata from 2.5.0 to 3.0.0 (#1477)

chore(deps): bump slackapi/slack-github-action from 2.1.1 to 3.0.1 (#1476)

chore(deps): bump codecov/codecov-action from 5.5.2 to 6.0.0 (#1475)

chore(deps): bump actions/download-artifact from 8.0.0 to 8.0.1 (#1474)

refactor: rename AttachingAgentKwargs middleware to AttachingConversationKwargs (#1473)

chore: improve type checking behavior (#1470)

fix(assistant): get_thread_context calls store.find() for user_message events (#1453)

chore: fix test warnings across test suite (#1468)

chore: replace sleep-based polling with Event synchronization in tests (#1467)

fix: Remove 'agent: BoltAgent' listener argument (#1466)

feat: surface the set_status argument to listeners if required event details are available (#1465)

fix: improve the robustness of the payload extract logic (#1464)

feat: add support for say_stream utility (#1462)