Bump the base crate to 2024 edition and use let-chains in there

[bnjbvr]

…which requires the base crate to use the 2024 edition.

[bnjbvr]

Reverting to draft at the moment; we should first land the Ruma bump, otherwise this will cause some unnecessary rebase pain for the author.

[codecov]

Codecov Report

Attention: Patch coverage is 86.89024% with 43 lines in your changes missing coverage. Please review.

Project coverage is 88.86%. Comparing base (bcb4ab4) to head (36059b3).
Report is 4 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-base/src/room/room_info.rs	13.88%	22 Missing and 9 partials ⚠️
...base/src/response_processors/e2ee/tracked_users.rs	66.66%	0 Missing and 4 partials ⚠️
crates/matrix-sdk-base/src/store/memory_store.rs	73.33%	0 Missing and 4 partials ⚠️
...tes/matrix-sdk-base/src/store/integration_tests.rs	94.23%	0 Missing and 3 partials ⚠️
crates/matrix-sdk-base/src/latest_event.rs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5431      +/-   ##
==========================================
- Coverage   88.86%   88.86%   -0.01%     
==========================================
  Files         333      333              
  Lines       91374    91402      +28     
  Branches    91374    91402      +28     
==========================================
+ Hits        81199    81223      +24     
- Misses       6351     6355       +4     
  Partials     3824     3824              

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[jplatte]

Other than CI failing due to the no-longer-used OptionExt trait, and my (very much not important) nit above, LGTM.