Prepare our /keys/claim response handling to handle multiple OTKs

[poljar]

This is useful if we ever decide to switch to X3DH for the session establishment. It also refactors a bit the /keys/claim response handling method.

[codecov]

Codecov Report

Attention: 17 lines in your changes are missing coverage. Please review.

Comparison is base (c7712b5) 82.45% compared to head (56c19bc) 82.46%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
...rates/matrix-sdk-crypto/src/types/one_time_keys.rs	33.33%	8 Missing ⚠️
crates/matrix-sdk-crypto/src/olm/account.rs	80.64%	6 Missing ⚠️
.../matrix-sdk-crypto/src/session_manager/sessions.rs	93.47%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2870   +/-   ##
=======================================
  Coverage   82.45%   82.46%           
=======================================
  Files         211      211           
  Lines       21615    21639   +24     
=======================================
+ Hits        17823    17844   +21     
- Misses       3792     3795    +3     

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