Support for MSC4388 for the QR login

[poljar]

• Public API changes documented in changelogs (optional)

[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.01%. Comparing base (acda2e8) to head (6fc3247).
⚠️ Report is 45 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...cation/oauth/qrcode/rendezvous_channel/msc_4388.rs	95.79%	11 Missing and 2 partials ⚠️
...tion/oauth/qrcode/secure_channel/crypto_channel.rs	67.85%	0 Missing and 9 partials ⚠️
.../authentication/oauth/qrcode/secure_channel/mod.rs	94.44%	4 Missing and 4 partials ⚠️
...hentication/oauth/qrcode/rendezvous_channel/mod.rs	89.47%	0 Missing and 4 partials ⚠️
...atrix-sdk/src/authentication/oauth/qrcode/grant.rs	98.26%	0 Missing and 2 partials ⚠️
...atrix-sdk/src/authentication/oauth/qrcode/login.rs	99.21%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6173      +/-   ##
==========================================
+ Coverage   89.91%   90.01%   +0.10%     
==========================================
  Files         374      375       +1     
  Lines      102613   103414     +801     
  Branches   102613   103414     +801     
==========================================
+ Hits        92267    93092     +825     
+ Misses       6783     6765      -18     
+ Partials     3563     3557       -6     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

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_{Comparing poljar/qr-login/msc4388 (6fc3247) with main (81bed18)}