Rounding strategy for slot duration at JSON export

Implements #16 (closed)

AKModel/models.py

+import decimal
 import itertools
 import json
+import math
 from dataclasses import dataclass
 from datetime import datetime, timedelta
 from typing import Iterable, Generator
@@ -934,10 +936,12 @@ class AKSlot(models.Model):
                 return []
             return [f"availability-person-{owner.pk}"]
 
+        ceil_offet_eps = decimal.Decimal(1e-4)
+
         # self.slots_in_an_hour is set in AKJSONExportView
         data = {
             "id": str(self.pk),
-            "duration": round(self.duration * self.slots_in_an_hour),
+            "duration": math.ceil(self.duration * self.slots_in_an_hour - ceil_offet_eps),
             "properties": {},
             "room_constraints": [constraint.name
                                  for constraint in self.ak.requirements.all()],
@@ -948,6 +952,7 @@ class AKSlot(models.Model):
                                    for owner in self.ak.owners.all()]),
                 "description": self.ak.description,
                 "reso": self.ak.reso,
+                "duration_in_hours": float(self.duration),
                 },
             }