Fix implementation for balance_of (#79)

The balance_of syscall is now available in pallet-revive.
- Fix balance_of implementation to use correct runtime api
- Add build_address_argument_store helper to be used for address arguments

crates/llvm-context/src/polkavm/context/mod.rs

@@ -607,6 +607,23 @@ where
         Pointer::new(r#type, AddressSpace::Stack, pointer)
     }
 
+    /// Truncate `address` to the ethereum address length and store it as bytes on the stack.
+    /// The stack allocation will be at the function entry. Returns the stack pointer.
+    /// This helper should be used when passing address arguments to the runtime, ensuring correct size and endianness.
+    pub fn build_address_argument_store(
+        &self,
+        address: inkwell::values::IntValue<'ctx>,
+    ) -> anyhow::Result<Pointer<'ctx>> {
+        let address_type = self.integer_type(revive_common::BIT_LENGTH_ETH_ADDRESS);
+        let address_pointer = self.build_alloca_at_entry(address_type, "address_pointer");
+        let address_truncated =
+            self.builder()
+                .build_int_truncate(address, address_type, "address_truncated")?;
+        let address_swapped = self.build_byte_swap(address_truncated.into())?;
+        self.build_store(address_pointer, address_swapped)?;
+        Ok(address_pointer)
+    }
+
     /// Load the address at given pointer and zero extend it to the VM word size.
     pub fn build_load_address(
         &self,