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

server/common/constants.py

@@ -1,30 +0,0 @@
-from enum import Enum
-
-
-class AugmentedEnum(Enum):
-    def __hash__(self):
-        return self.value.__hash__()
-
-    def __eq__(self, other):
-        if isinstance(other, type(self)) or isinstance(other, str):
-            return self.value == other
-        return False
-
-    def __str__(self) -> str:
-        return self.value
-
-
-class Axis(AugmentedEnum):
-    OBS = "obs"
-    VAR = "var"
-
-
-class DiffExpMode(AugmentedEnum):
-    TOP_N = "topN"
-    VAR_FILTER = "varFilter"
-
-
-JSON_NaN_to_num_warning_msg = "JSON encoding failure - please verify all data are finite values (no NaN or Infinities)"
-REACTIVE_LIMIT = 1_000_000
-
-MAX_LAYOUTS = 30