Add support for linking new devices in the QRCodeLoginScreen.

[pixlwave]

Notes:

• Based on https://github.com/hughns/element-x-ios/tree/msc4108-v2025 (although some of this is already in the app now from previous PRs).

• There's still SDK updates required for this such as feat(sdk,ffi): add CheckCodeSender::validate() matrix-org/matrix-rust-sdk#5957 (but everything is behind a feature flag so it is safe to merge).

• I've only tested the "Link Mobile Device" flow. I believe linking against EW needs a specific build.

• Still needs some unit tests, but preview tests are there.

[github-actions]

	Warnings
⚠️	You seem to have made changes to views. Please consider adding screenshots.

Generated by 🚫 Danger Swift against 20505d2

[codecov]

Codecov Report

❌ Patch coverage is 52.38095% with 250 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.41%. Comparing base (6153480) to head (20505d2).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...QRCodeLoginScreen/QRCodeLoginScreenViewModel.swift	32.00%	102 Missing ⚠️
...tensions/AVMetadataMachineReadableCodeObject.swift	49.47%	48 Missing ⚠️
...ervices/Authentication/AuthenticationService.swift	0.00%	30 Missing ⚠️
...lowCoordinators/LinkNewDeviceFlowCoordinator.swift	0.00%	19 Missing ⚠️
...Services/Authentication/LinkNewDeviceService.swift	26.66%	11 Missing ⚠️
...owCoordinators/AuthenticationFlowCoordinator.swift	0.00%	8 Missing ⚠️
...CodeLoginScreen/QRCodeLoginScreenCoordinator.swift	0.00%	8 Missing ⚠️
...ens/QRCodeLoginScreen/View/QRCodeScannerView.swift	0.00%	8 Missing ⚠️
...ns/QRCodeLoginScreen/QRCodeLoginScreenModels.swift	89.23%	7 Missing ⚠️
...ens/QRCodeLoginScreen/View/QRCodeLoginScreen.swift	95.53%	5 Missing ⚠️
... and 1 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4891      +/-   ##
===========================================
- Coverage    79.49%   79.41%   -0.09%     
===========================================
  Files          892      892              
  Lines        65040    65319     +279     
===========================================
+ Hits         51705    51870     +165     
- Misses       13335    13449     +114     

Flag	Coverage Δ
unittests	71.22% <52.38%> (-0.07%)	⬇️

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