feat: add native balance in StorageChanges (#292)

* feat: add native balance in StorageChanges

This will be used by the next update of DCI to properly track native balance for all the contract that it's indexing. Also added a performance optimization, we now ignore slot updates if the value after the transaction is the same than before.

* docs: add docs on how to generate test assets

---------

Co-authored-by: zizou <111426680+flopell@users.noreply.github.com>

substreams/crates/tycho-substreams/src/testing/mock_store.rs

@@ -0,0 +1,95 @@
+//! Contains a mock store for internal testing.
+//!
+//! Might make this public alter to users can test their store handlers.
+use std::{cell::RefCell, collections::HashMap, rc::Rc};
+use substreams::{
+    prelude::{BigInt, StoreDelete, StoreGet, StoreNew},
+    store::StoreAdd,
+};
+
+type BigIntStore = HashMap<String, Vec<(u64, BigInt)>>;
+
+#[derive(Debug, Clone)]
+pub struct MockStore {
+    data: Rc<RefCell<BigIntStore>>,
+}
+
+impl StoreDelete for MockStore {
+    fn delete_prefix(&self, _ord: i64, prefix: &String) {
+        self.data
+            .borrow_mut()
+            .retain(|k, _| !k.starts_with(prefix));
+    }
+}
+
+impl StoreNew for MockStore {
+    fn new() -> Self {
+        Self { data: Rc::new(RefCell::new(HashMap::new())) }
+    }
+}
+
+impl StoreAdd<BigInt> for MockStore {
+    fn add<K: AsRef<str>>(&self, ord: u64, key: K, value: BigInt) {
+        let mut guard = self.data.borrow_mut();
+        guard
+            .entry(key.as_ref().to_string())
+            .and_modify(|v| {
+                let prev_value = v.last().unwrap().1.clone();
+                v.push((ord, prev_value + value.clone()));
+            })
+            .or_insert(vec![(ord, value)]);
+    }
+
+    fn add_many<K: AsRef<str>>(&self, _ord: u64, _keys: &Vec<K>, _value: BigInt) {
+        todo!()
+    }
+}
+
+impl StoreGet<BigInt> for MockStore {
+    fn new(_idx: u32) -> Self {
+        Self { data: Rc::new(RefCell::new(HashMap::new())) }
+    }
+
+    fn get_at<K: AsRef<str>>(&self, ord: u64, key: K) -> Option<BigInt> {
+        self.data
+            .borrow()
+            .get(&key.as_ref().to_string())
+            .map(|v| {
+                v.iter()
+                    .find(|(current_ord, _)| *current_ord == ord)
+                    .unwrap()
+                    .1
+                    .clone()
+            })
+    }
+
+    fn get_last<K: AsRef<str>>(&self, key: K) -> Option<BigInt> {
+        self.data
+            .borrow()
+            .get(&key.as_ref().to_string())
+            .map(|v| v.last().unwrap().1.clone())
+    }
+
+    fn get_first<K: AsRef<str>>(&self, key: K) -> Option<BigInt> {
+        self.data
+            .borrow()
+            .get(&key.as_ref().to_string())
+            .map(|v| v.first().unwrap().1.clone())
+    }
+
+    fn has_at<K: AsRef<str>>(&self, ord: u64, key: K) -> bool {
+        self.data
+            .borrow()
+            .get(&key.as_ref().to_string())
+            .map(|v| v.iter().any(|(v, _)| *v == ord))
+            .unwrap_or(false)
+    }
+
+    fn has_last<K: AsRef<str>>(&self, _key: K) -> bool {
+        todo!()
+    }
+
+    fn has_first<K: AsRef<str>>(&self, _key: K) -> bool {
+        todo!()
+    }
+}