feat: Add NativeCurrency trait and implement for Ether

Introduced `NativeCurrency` trait representing native blockchain currencies. Implemented this trait for `Ether` and updated the `prelude` and entity modules accordingly.

src/entities/ether.rs

@@ -4,6 +4,8 @@ use crate::prelude::*;
 /// Represents the native currency of the blockchain.
 pub type Ether = CurrencyLike<true, Option<Token>>;
 
+impl NativeCurrency for Ether {}
+
 impl Currency for Ether {
     /// Retrieves the address associated with the currency.
     #[inline]

src/entities/mod.rs

@@ -2,5 +2,6 @@ pub mod base_currency;
 pub mod currency;
 pub mod ether;
 pub mod fractions;
+pub mod native_currency;
 pub mod token;
 pub mod weth9;

src/entities/native_currency.rs

@@ -0,0 +1,12 @@
+use crate::prelude::*;
+
+/// Represents the native currency of the chain on which it resides
+pub trait NativeCurrency: Currency {
+    fn is_native(&self) -> bool {
+        true
+    }
+
+    fn is_token(&self) -> bool {
+        false
+    }
+}

src/prelude.rs

@@ -11,6 +11,7 @@ pub use crate::{
             percent::Percent,
             price::Price,
         },
+        native_currency::NativeCurrency,
         token::Token,
         weth9::WETH9,
     },