Seal concluded livestream and allow final activity without streamSequence

[compulim]

Fixes #5268.

Changelog Entry

Fixed

• Fixes #5268. Concluded livestream is sealed and activities received afterwards are ignored, and streamSequence is not required in final activity, in PR #5273, by @compulim

Description

Concluded livestream should not be open to any further incoming activities.

Also, final activity in the livestream do not requires channelData.streamSequence to be set. It will be assumed Infinity so it is always the last one.

Design

channelData.streamSequence is useful for out-of-order interim activities. But for final activities, as it always conclude the livestream and seal from further activities, streamSequence is not used in the scenario. Thus, we are taking away this requirement.

Specific Changes

• Updated activities reducer to ignore activities for concluded livestream
• Updated getActivityLivestreamMetadata to relax streamSequence for final activity

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)