Delivery/read receipts not consistently collapsed

[cdenyar]

• I have searched open and closed issues for duplicates
• I am submitting a bug report for existing functionality that does not work as intended
• I have read https://github.com/signalapp/Signal-Android/wiki/Submitting-useful-bug-reports
• This isn't a feature request or a discussion topic

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Bug description

Some contacts consistently show delivery/read receipts for each successive message even when sent within seconds and show 'NOW', others consistently combine/collapse the receipts for successive messages.

Steps to reproduce

• Send contact several messages quickly
• Observe some contacts the receipt icons only show on the bottom message to indicate delivered/read for the set, others consistently show the receipt on every message.

Actual result: Receipt icons not always collapsed for quickly sent successive messages.
Expected result: Receipt icons for quickly sent successive messages with the same status combine/collapse the receipt status icon into the most recently sent message.

Screenshots

Examples where contact messages consistently show receipt on each message:

Example where successive messages share a receipt status:

Device info

Device: Pixel 2 XL
Android version: 9
Signal version: 4.36.2

Link to debug log

https://debuglogs.org/4448519c8eccc59f969a4da1edee3892bcf743a49d993b49b7c911e1cc17d735

[greyson-signal]

We only collapse footers when they would otherwise be the same. For disappearing messages, they're never the same -- each message has their own timer. Therefore, we can't collapse them.