refactor: update backend module and demo notebook for histogram computation

Author: ElouenGinat

docs/core/index.rst

@@ -11,4 +11,4 @@ Main Modules
   :recursive:
   :nosignatures:
 
-  cli_adapter
+  backend

sandbox/khisto_demo.ipynb

@@ -475,10 +475,10 @@
     }
    ],
    "source": [
-    "from khisto.core import compute_histogram\n",
+    "from khisto.core import compute_histograms\n",
     "\n",
     "# Get all granularity levels\n",
-    "results = compute_histogram(data)\n",
+    "results = compute_histograms(data)\n",
     "\n",
     "print(f\"Number of granularity levels: {len(results)}\")\n",
     "print(\"\\nGranularity levels:\")\n",