feat(erc721): implement erc-721 token standard

contracts/Cargo.toml

@@ -15,9 +15,12 @@ alloy-sol-types = { version = "0.3.1", default-features = false }
 stylus-sdk = { version = "0.4.3", default-features = false }
 stylus-proc = { version = "0.4.3", default-features = false }
 mini-alloc = "0.4.2"
+derive_more = "0.99.17"
 
 [dev-dependencies]
 grip = { path = "../lib/grip" }
+rand = "0.8.5"
+once_cell = "1.19.0"
 
 [features]
 default = []

contracts/src/arithmetic.rs

@@ -0,0 +1,24 @@
+use alloy_primitives::U256;
+use stylus_sdk::storage::{StorageGuardMut, StorageUint};
+
+pub(crate) trait AddAssignUnchecked<T> {
+    fn add_assign_unchecked(&mut self, rhs: T);
+}
+
+impl<'a> AddAssignUnchecked<U256> for StorageGuardMut<'a, StorageUint<256, 4>> {
+    fn add_assign_unchecked(&mut self, rhs: U256) {
+        let new_balance = self.get() + rhs;
+        self.set(new_balance);
+    }
+}
+
+pub(crate) trait SubAssignUnchecked<T> {
+    fn sub_assign_unchecked(&mut self, rhs: T);
+}
+
+impl<'a> SubAssignUnchecked<U256> for StorageGuardMut<'a, StorageUint<256, 4>> {
+    fn sub_assign_unchecked(&mut self, rhs: U256) {
+        let new_balance = self.get() - rhs;
+        self.set(new_balance);
+    }
+}

contracts/src/erc20/mod.rs

@@ -142,7 +142,7 @@ impl ERC20 {
         value: U256,
     ) -> Result<bool, Error> {
         let from = msg::sender();
-        if to == Address::ZERO {
+        if to.is_zero() {
             return Err(Error::InvalidReceiver(ERC20InvalidReceiver {
                 receiver: Address::ZERO,
             }));
@@ -200,7 +200,7 @@ impl ERC20 {
         value: U256,
     ) -> Result<bool, Error> {
         let owner = msg::sender();
-        if spender == Address::ZERO {
+        if spender.is_zero() {
             return Err(Error::InvalidSpender(ERC20InvalidSpender {
                 spender: Address::ZERO,
             }));
@@ -246,12 +246,12 @@ impl ERC20 {
         to: Address,
         value: U256,
     ) -> Result<bool, Error> {
-        if from == Address::ZERO {
+        if from.is_zero() {
             return Err(Error::InvalidSender(ERC20InvalidSender {
                 sender: Address::ZERO,
             }));
         }
-        if to == Address::ZERO {
+        if to.is_zero() {
             return Err(Error::InvalidReceiver(ERC20InvalidReceiver {
                 receiver: Address::ZERO,
             }));