Inline all format arguments where possible

This makes code more readale and concise,
moving all format arguments like `format!("{}", foo)`
into the more compact `format!("{foo}")` form.

The change was automatically created with, so there are far less change
of an accidental typo.

```
cargo clippy --fix -- -A clippy::all -W clippy::uninlined_format_args
```

crates/test-utils/src/assert_linear.rs

@@ -83,7 +83,7 @@ impl Round {
 
         let a = mean_y - b * mean_x;
 
-        self.plot = format!("y_pred = {:.3} + {:.3} * x\n\nx     y     y_pred\n", a, b);
+        self.plot = format!("y_pred = {a:.3} + {b:.3} * x\n\nx     y     y_pred\n");
 
         let mut se = 0.0;
         let mut max_error = 0.0f64;