feat(sdk): Expose a local server builder

[zecakeh]

This exposes the server builder code that was used behind the sso-login feature so that it can be reused in other places, like during OAuth 2.0 login. It's called LocalServerBuilder and is behind the local-server feature.

I added types around the channels to make the API easier to use and harder to misuse (if the shutdown signal is not sent, the server will keep running). They are inspired by tokio's JoinHandle and AbortHandle.

[codecov]

Codecov Report

Attention: Patch coverage is 87.23404% with 12 lines in your changes missing coverage. Please review.

Project coverage is 86.43%. Comparing base (cabb345) to head (b720ac2).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/utils/local_server.rs	90.69%	8 Missing ⚠️
...rix-sdk/src/authentication/matrix/login_builder.rs	50.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4804      +/-   ##
==========================================
+ Coverage   86.40%   86.43%   +0.03%     
==========================================
  Files         295      296       +1     
  Lines       34458    34498      +40     
==========================================
+ Hits        29772    29819      +47     
+ Misses       4686     4679       -7     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Hywan]

I think this is a great improvement. Thanks for your work!