Support for MSC4388 for the QR login

[poljar]

• Public API changes documented in changelogs (optional)

[codecov]

Codecov Report

❌ Patch coverage is 93.59684% with 81 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.00%. Comparing base (1136eb4) to head (d8cd83f).
⚠️ Report is 65 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	94.76%	11 Missing and 6 partials ⚠️
...atrix-sdk/src/authentication/oauth/qrcode/grant.rs	92.69%	14 Missing and 2 partials ⚠️
...atrix-sdk/src/authentication/oauth/qrcode/login.rs	95.77%	10 Missing and 2 partials ⚠️
.../authentication/oauth/qrcode/secure_channel/mod.rs	93.42%	6 Missing and 4 partials ⚠️
...tion/oauth/qrcode/secure_channel/crypto_channel.rs	67.85%	0 Missing and 9 partials ⚠️
...hentication/oauth/qrcode/rendezvous_channel/mod.rs	88.00%	0 Missing and 6 partials ⚠️
...s/matrix-sdk-crypto/src/types/qr_login/msc_4388.rs	87.50%	3 Missing and 2 partials ⚠️
.../matrix-sdk/src/authentication/oauth/qrcode/mod.rs	96.89%	4 Missing ⚠️
crates/matrix-sdk-crypto/src/types/qr_login/mod.rs	71.42%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6173      +/-   ##
==========================================
+ Coverage   89.94%   90.00%   +0.06%     
==========================================
  Files         381      382       +1     
  Lines      105753   106793    +1040     
  Branches   105753   106793    +1040     
==========================================
+ Hits        95115    96121    +1006     
- Misses       6993     7013      +20     
- Partials     3645     3659      +14     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

---

_{Comparing poljar/qr-login/msc4388 (d8cd83f) with main (2ec031b)}

[hughns]

// n.b. this doesn't match the MSC which says that it is a server name not the base URL
// Should be something like self.client.user_id_server_name()