feat(encryption): Add high-level API for Device Dehydration (MSC3814)

[thmasq]

This introduces a high-level interface for Device Dehydration, which allows clients to proactively create a virtual device on the server to receive E2EE keys while the primary client is offline. Currently the only way to use this is with the raw bindings of the ruma crate.

The new functionality is exposed via client.encryption().dehydrated_devices() and provides upload and rehydrate_and_absorb methods. All new additions are gated behind the unstable-msc3814 cargo feature.

As I'm unfamiliar with wiremock, I had some AI assistance when making the integration tests. I'm currently running them like the following:

cargo test -p matrix-sdk --test integration --features unstable-msc3814,testing dehydrated_devices

• I've documented the public API Changes in the appropriate CHANGELOG.md files.
• This PR was made with the help of AI.

Signed-off-by: Thomas Q thomasqsa@gmail.com

[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

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_{Comparing thmasq:feat-msc3814 (b6c851b) with main (a99e79a)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.90%. Comparing base (a48f238) to head (b6c851b).
⚠️ Report is 12 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Coverage   89.90%   89.90%           
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  Files         373      374    +1     
  Lines      102570   102613   +43     
  Branches   102570   102613   +43     
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+ Hits        92219    92259   +40     
+ Misses       6790     6787    -3     
- Partials     3561     3567    +6     

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