ENG-8715.

This differential is doing two things:

1. Renaming decryptSequentialAndPersist -> decryptAndPersist in OlmAPI to properly reflect what this code method is now doing.
2. Using decrypt instead of decrypt_sequential from olm which is an actual change, stops requiring sequential messages.

This might cause some messages to arrive in an inverted order, and we're planning to handle this here: https://linear.app/comm/issue/ENG-8752/update-the-reducers-to-respect-properties-timestamps

This is just swapping back to the decrypt method which is used elsewhere in the codebase and has the same params and return type so this should work out of the box. Under the hood, we only avoid one additional check (src).