Implement helpers for relative balances.

Adds some helpers that will users help to convert relative balances changes to absolute ones.

The goal is to make this as reduce the effort of the user to  implementing a simple map handler that extracts relative balances changes.

crates/tycho-substreams/rustfmt.toml

@@ -0,0 +1,13 @@
+reorder_imports = true
+imports_granularity = "Crate"
+use_small_heuristics = "Max"
+comment_width = 100
+wrap_comments = true
+binop_separator = "Back"
+trailing_comma = "Vertical"
+trailing_semicolon = false
+use_field_init_shorthand = true
+chain_width = 40
+ignore = [
+    "src/pb",
+]