Weather implementation (#260)

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## Description

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you want here. -->

An implementation of basic weather systems.

The weather component attached to a world instance would be handled for
all clients, except those that have their own weather component; these
clients would be handled separately.

## Test Plan

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used to test this. -->
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playground, replace the playground section with a note that indicates
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<details>

<summary>Playground</summary>

```rust
fn handle_command_events(
    instances: Query<Entity, With<Instance>>,
    mut exec_cmds: EventReader<CommandExecution>,
    mut commands: Commands,
) {
    for cmd in exec_cmds.iter() {
        let msg = cmd.command.to_string();
        let ent = instances.single();

        match msg.as_str() {
            "ar" => {
                commands.entity(ent).insert(Rain(WEATHER_LEVEL.end));
            }
            "rr" => {
                commands.entity(ent).remove::<Rain>();
            }
            "at" => {
                commands.entity(ent).insert(Thunder(WEATHER_LEVEL.end));
            }
            "rt" => {
                commands.entity(ent).remove::<Thunder>();
            }
            _ => (),
        };
    }
}
```

</details>

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using a playground. -->
Steps:
1. Run `cargo test --package valence --lib -- weather::test`

#### Related
Part of #210
Past approach #106

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fixes. -->

crates/valence/src/lib.rs

@@ -43,6 +43,7 @@ pub mod server;
 mod unit_test;
 pub mod util;
 pub mod view;
+pub mod weather;
 
 pub mod prelude {
  pub use async_trait::async_trait;

crates/valence/src/server.rs

@@ -30,6 +30,7 @@ use crate::player_list::PlayerListPlugin;
 use crate::prelude::event::ClientEventPlugin;
 use crate::prelude::ComponentPlugin;
 use crate::server::connect::do_accept_loop;
+use crate::weather::WeatherPlugin;
 
 mod byte_channel;
 mod connect;
@@ -335,7 +336,8 @@ pub fn build_plugin(
  .add_plugin(EntityPlugin)
  .add_plugin(InstancePlugin)
  .add_plugin(InventoryPlugin)
- .add_plugin(PlayerListPlugin);
+ .add_plugin(PlayerListPlugin)
+ .add_plugin(WeatherPlugin);
 
  /*
  println!(