Rework events

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](bevyengine/bevy#12936)
  which we also can do. It won't be that noticeable since user register
  much less amount of replicon events, but nice to have.

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Custom events now registered with serialization and deserialization functions instead of systems. This makes the API more convenient since the purpose of custom systems was to customize serialization.
+- All events are processed in one system instead of a separate system for each event. Bevy does a [similar optimization](https://github.com/bevyengine/bevy/pull/12936) for event updates. It won't be that noticeable since user register much less amount of replicon events.
+
 ## [0.25.2] - 2024-05-18
 
 ### Fixed

src/client.rs

@@ -13,10 +13,8 @@ use varint_rs::VarintReader;
 use crate::core::{
     command_markers::{CommandMarkers, EntityMarkers},
     common_conditions::{client_connected, client_just_connected, client_just_disconnected},
-    replication_fns::{
-        ctx::{DespawnCtx, RemoveCtx, WriteCtx},
-        ReplicationFns,
-    },
+    ctx::{DespawnCtx, RemoveCtx, WriteCtx},
+    replication_fns::ReplicationFns,
     replicon_channels::{ReplicationChannel, RepliconChannels},
     replicon_tick::RepliconTick,
     Replicated,