refactor: simplify Repository and Serde traits, introduce AnyRepository, remove ProtobufSerde

[ar3s3ru]

• feat(aggregate::repository): expose single Repository trait, add AnyRepository extension
• refactor: use new Repository unified trait, switch to AnyRepository in examples
• refactor(serde): unify the Serde trait, remove serde-protobuf feature
• refactor(eventually): move to nested, local mod.rs pattern

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (f04295a) 87.33% compared to head (191273c) 91.53%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
...entually/src/aggregate/repository/event_sourced.rs	89.58%	5 Missing ⚠️
eventually/src/aggregate/repository/any.rs	90.00%	2 Missing ⚠️
eventually/src/tracing.rs	0.00%	2 Missing ⚠️
eventually/src/aggregate/repository/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #270      +/-   ##
==========================================
+ Coverage   87.33%   91.53%   +4.19%     
==========================================
  Files          17       17              
  Lines        1161     1158       -3     
==========================================
+ Hits         1014     1060      +46     
+ Misses        147       98      -49     

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