Enable Rust Crypto for all users

[Anderas]

In this final stage of Rust Crypto rollout enable the feature to all users. The feature flags mechanism and other now-unnecessary code will be removed in future PRs

Note that this change will be released as "hotfix" to only contain the target percentage change and no other features

[pixlwave]

🚀🚀🚀

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (hotfix/1.10.9@9b2c7a6). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff                @@
##             hotfix/1.10.9    #7485   +/-   ##
================================================
  Coverage                 ?   12.29%           
================================================
  Files                    ?     1645           
  Lines                    ?   163155           
  Branches                 ?    66992           
================================================
  Hits                     ?    20066           
  Misses                   ?   142439           
  Partials                 ?      650           

Flag	Coverage Δ
uitests	55.24% <0.00%> (?)

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[bhauer]

FYI: This has been cited as potentially causing an issue when iOS clients send (a) a photo followed by (b) a text message. See issues #24267 and #25221 on element-web:

element-hq/element-web#24267
element-hq/element-web#25221

Desktop clients will be unable to decrypt the (b) text, instead seeing "unable to decrypt message."

The situation can apparently escalate via an unknown sequence to cause severe encryption problems in the channel over time. I have one channel between just two users who have always trusted one another devolve into permanent cryptography failure. These users are both iOS+desktop users.