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/czi_hosted/data_cxg/cxg_util.py

@@ -0,0 +1,37 @@
+import numpy as np
+
+
+def pack_selector_from_mask(boolarray):
+    """
+    pack all contiguous selectors into slices.  Remember that
+    tiledb multi_index requires INCLUSIVE indices.
+    """
+
+    if boolarray is None:
+        return slice(None)
+
+    assert type(boolarray) == np.ndarray
+    assert boolarray.dtype == bool
+
+    selector = np.nonzero(boolarray)[0]
+    return pack_selector_from_indices(selector)
+
+
+def pack_selector_from_indices(selector):
+
+    if len(selector) == 0:
+        return None
+
+    result = []
+    current = slice(selector[0], selector[0])
+    for sel in selector[1:]:
+        if sel == current.stop + 1:
+            current = slice(current.start, sel)
+        else:
+            result.append(current if current.start != current.stop else current.start)
+            current = slice(sel, sel)
+
+    if len(result) == 0 or result[-1] != current:
+        result.append(current if current.start != current.stop else current.start)
+
+    return result