Rework messages serialization

[Shatur]

The performance is a bit slower, but we getting a free byte per changed entity and several bytes per message.
For example, in our statistic test we using only 16 bytes for a test message instead of 33.

While writing the documentation, I decided to rename InitMessage to ChangeMessage and UpdateMessage to MutateMessage (and related types). This change helps make it clear that MutateMessage stores only component mutations. In contrast, ChangeMessage stores any type of change and may even include mutations if there is an insertion or removal. I considered including the rename into a separate PR, but decided to keep it here since the messages got completely reworked.

I would recommend to start reading from change_message and mutate_message modules, they contain a lot of internal documentation and description about how the new approach works.

I also switched to plain Vec for serialization since we no longer need Cursor for it
and Writer::write_all is much slower then Vec::extend_from_slice.

[codecov]

Codecov Report

Attention: Patch coverage is 94.93007% with 29 lines in your changes missing coverage. Please review.

Project coverage is 90.40%. Comparing base (5ae9e5f) to head (024829f).

Files with missing lines	Patch %	Lines
src/client.rs	92.99%	11 Missing ⚠️
src/core/replication/replicated_clients.rs	87.50%	5 Missing ⚠️
src/core/event_registry/server_event.rs	69.23%	4 Missing ⚠️
src/server.rs	96.19%	4 Missing ⚠️
src/server/replication_messages/serialized_data.rs	91.17%	3 Missing ⚠️
src/server/replication_messages/change_message.rs	98.34%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #352      +/-   ##
==========================================
+ Coverage   89.98%   90.40%   +0.41%     
==========================================
  Files          41       44       +3     
  Lines        2367     2417      +50     
==========================================
+ Hits         2130     2185      +55     
+ Misses        237      232       -5     

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