Use symmetric difference iterator (#11)

Implements https://github.com/cerc-io/go-ethereum/issues/319

With this we can perform a single pass to process updates.

Also
* refactor code structure around single-pass iteration
* refactor builder metrics to match new set of functions
* fix unit tests by running sequentially
* update ipld-eth-db in compose
* factor out fixture data into external module
* some CI updates

Reviewed-on: https://git.vdb.to/cerc-io/plugeth-statediff/pulls/11

Makefile

@@ -9,7 +9,8 @@ $(MOCKS_DIR)/gen_backend.go:
 		github.com/openrelayxyz/plugeth-utils/core Backend,Downloader
 
 docker-image: mocks
-	docker build . -t "cerc/plugeth-statediff:local"
+	docker build . -t "cerc/plugeth-statediff:local" \
+		--build-arg GIT_VDBTO_TOKEN
 .PHONY: docker-image
 
 # Local build