fix: Replace smart pointer with regular pointer

Apparently was not necessary and was causing clippy warnings.

```
warning: you seem to be trying to use `&Box<T>`. Consider using just `&T`
  --> src/encoding/models.rs:91:32
   |
91 |     pub protocol_state: Option<&'a Box<dyn ProtocolSim>>,
   |                                ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&'a dyn ProtocolSim`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#borrowed_box
   = note: `#[warn(clippy::borrowed_box)]` on by default
   ```

examples/uniswapx-encoding-example/main.rs

@@ -167,7 +167,6 @@ fn main() {
     println!(" ====== Simple swap DAI -> USDT ======");
     println!(
         "The following callback data should be sent to the filler contract, along with the \
-        encoded order and signature: {:?}",
-        hex_calldata
+        encoded order and signature: {hex_calldata:?}"
     );
 }

src/encoding/models.rs

@@ -88,7 +88,7 @@ pub struct Swap<'a> {
     pub user_data: Option<Bytes>,
     /// Optional protocol state used to perform the swap.
     #[serde(skip)]
-    pub protocol_state: Option<&'a Box<dyn ProtocolSim>>,
+    pub protocol_state: Option<&'a dyn ProtocolSim>,
 }
 
 impl<'a> Swap<'a> {
@@ -98,7 +98,7 @@ impl<'a> Swap<'a> {
         token_out: Bytes,
         split: f64,
         user_data: Option<Bytes>,
-        protocol_state: Option<&'a Box<dyn ProtocolSim>>,
+        protocol_state: Option<&'a dyn ProtocolSim>,
     ) -> Self {
         Self { component: component.into(), token_in, token_out, split, user_data, protocol_state }
     }