refactor(engine): use Rust edition 2021

This change is because of a rustfmt bug in the 2024 edition.

For example, the following code snippet:
```
struct Value {}
struct ParsingError {}
trait Keyword {}

impl Value {
    fn parse<KeywordT: Keyword>(value: &str, line_no: usize) -> Result<Self, ParsingError> {
        todo!();
    }
}
```

when formatted with `rustfmt --edition 2021 --emit stdout --config max_width=90,brace_style=AlwaysNextLine` becomes:
```
struct Value {}
struct ParsingError {}
trait Keyword {}

impl Value
{
    fn parse<KeywordT: Keyword>(value: &str, line_no: usize)
    -> Result<Self, ParsingError>
    {
        todo!();
    }
}
```

1 files changed, 12 insertions, 9 deletions

diff --git a/engine/src/renderer/main_render_pass.rs b/engine/src/renderer/main_render_pass.rs
index abd1022..04050f8 100644
--- a/engine/src/renderer/main_render_pass.rs
+++ b/engine/src/renderer/main_render_pass.rs
@@ -1,9 +1,8 @@
+use crate::asset::Assets;
+use crate::draw_flags::{DrawFlags, NoDraw, PolygonModeConfig};
 use crate::ecs::Query;
 use crate::ecs::query::term::{With, Without};
 use crate::ecs::sole::Single;
-
-use crate::asset::Assets;
-use crate::draw_flags::{DrawFlags, NoDraw, PolygonModeConfig};
 use crate::model::{MaterialSearchResult, Model};
 use crate::renderer::object::{Id as RendererObjectId, Store as RendererObjectStore};
 use crate::renderer::{
@@ -192,9 +191,13 @@ pub fn add_main_render_passes(
                 ));
             }
 
-            if let Some(draw_flags) = draw_flags.as_deref()
-                && draw_flags.polygon_mode_config != PolygonModeConfig::default()
-            {
+            if let Some(draw_flags) = draw_flags.as_deref().and_then(|draw_flags| {
+                if draw_flags.polygon_mode_config != PolygonModeConfig::default() {
+                    Some(draw_flags)
+                } else {
+                    None
+                }
+            }) {
                 render_pass
                     .commands
                     .push(RendererCommand::UpdateDrawProperties(
@@ -223,9 +226,9 @@ pub fn add_main_render_passes(
                 RendererDrawMeshOptions::default(),
             ));
 
-            if let Some(draw_flags) = draw_flags.as_deref()
-                && draw_flags.polygon_mode_config != PolygonModeConfig::default()
-            {
+            if draw_flags.as_deref().is_some_and(|draw_flags| {
+                draw_flags.polygon_mode_config != PolygonModeConfig::default()
+            }) {
                 render_pass
                     .commands
                     .push(RendererCommand::UpdateDrawProperties(