Rework events

[Shatur]

Superseded #259.

Events was implemented this way since the initial release of replicon (it was more then a year ago, time flies quickly!), but it have some flaws:

• Public API for custom ser/de require user to define the whole sending and receiving functions which is not ergonomic. It's especially bad for server events where user need to use a few public helpers that we provided to reduce the boilerplate.
• It creates a new set of systems for each replicon event. It's not very efficient and Bevy recently did a nice optimization which we also can do. It won't be that noticeable since user register much less amount of replicon events, but nice to have.

I think it's time to revisit the implementation and fix the mentioned flaws.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 89.04429% with 47 lines in your changes are missing coverage. Please review.

Project coverage is 90.86%. Comparing base (fc189a7) to head (868fca4). Report is 1 commits behind head on master.

Files	Patch %	Lines
src/server_event.rs	87.65%	30 Missing :warning:
src/client_event.rs	90.11%	17 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #262 +/- ## ========================================== + Coverage 90.79% 90.86% +0.06% ========================================== Files 37 36 -1 Lines 2076 2310 +234 ========================================== + Hits 1885 2099 +214 - Misses 191 211 +20 ```

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[Shatur]

Thanks! Ah, I forgot that you have a special use case... But yes, I think it would be better to implement this on your project side.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 89.04429% with 47 lines in your changes are missing coverage. Please review.

Project coverage is 90.86%. Comparing base (3146286) to head (868fca4).

:exclamation: Current head 868fca4 differs from pull request most recent head 9f77642

Please upload reports for the commit 9f77642 to get more accurate results.

Files	Patch %	Lines
src/server_event.rs	87.65%	30 Missing :warning:
src/client_event.rs	90.11%	17 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #262 +/- ## ========================================== + Coverage 90.83% 90.86% +0.03% ========================================== Files 37 36 -1 Lines 2084 2310 +226 ========================================== + Hits 1893 2099 +206 - Misses 191 211 +20 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.