Refactor czi_hosted and server into backend directory, pull common code into backend/common, refactor tests (#2102)

* move local_server -> backend/server server-> backend/czi_hosted, pull common code into backend/common update imports, tests and make commands

backend/common/Makefile

@@ -0,0 +1,11 @@
+
+.PHONY: unit-test
+unit-test:
+	PYTHONWARNINGS=ignore:ResourceWarning coverage run \
+		--source=fbs,utils \
+		--omit=.coverage,data_common/fbs/NetEncoding,venv \
+		-m unittest discover \
+		--start-directory ../test/test_common/unit \
+		--top-level-directory ../../ \
+		--verbose; test_result=$$?; \
+	exit $$test_result \