[roq-deribit] Round quantity and price for CreateOrder/ModifyOrder

[thraneh]

This change is prompted by Deribit's release note for the 22nd Oct: https://www.deribit.com/kb/22-october-2021

Order actions will be rejected if quantity or price isn't accurate.

It appears the release note only relates to the REST/WS interfaces.

As a precautionary measure, we implement this change for FIX.

The following examples are after the change has been implemented (field 38 is quantity and 44 is price):

CreateOrder

8=FIX.4.4|9=0000157|35=D|49=ROQ_TRADING|56=DERIBITSERVER|34=5|52=20211021-16:28:27.447|11=kAAC6QMAAQAA-bWA9hMX|54=1|38=1|44=63493.0|55=BTC-PERPETUAL|40=2|59=1|100010=roq-2-1001|10=077|

ModifyOrder

8=FIX.4.4|9=0000173|35=G|49=ROQ_TRADING|56=DERIBITSERVER|34=7|52=20211021-16:28:30.465|41=6759839183|11=BAAC6QMAAgAANsOu9hMX|60=20211021-16:28:27.449|54=1|38=1|40=2|44=63427.5|55=BTC-PERPETUAL|10=079|