Use FtPrecise in interest calculation

tests/leverage/test_interest.py

@@ -1,14 +1,14 @@
-from decimal import Decimal
 from math import isclose
 
 import pytest
 
 from freqtrade.leverage import interest
+from freqtrade.util import FtPrecise
 
 
-ten_mins = Decimal(1 / 6)
-five_hours = Decimal(5.0)
-twentyfive_hours = Decimal(25.0)
+ten_mins = FtPrecise(1 / 6)
+five_hours = FtPrecise(5.0)
+twentyfive_hours = FtPrecise(25.0)
 
 
 @pytest.mark.parametrize('exchange,interest_rate,hours,expected', [
@@ -28,11 +28,11 @@ twentyfive_hours = Decimal(25.0)
     ('ftx', 0.00025, twentyfive_hours, 0.015625),
 ])
 def test_interest(exchange, interest_rate, hours, expected):
-    borrowed = Decimal(60.0)
+    borrowed = FtPrecise(60.0)
 
     assert isclose(interest(
         exchange_name=exchange,
         borrowed=borrowed,
-        rate=Decimal(interest_rate),
+        rate=FtPrecise(interest_rate),
         hours=hours
     ), expected)