Unnecassarily large types in Datetime

[Brendan Hansknecht]

Some reason, we use I128 for each of the values in this struct:

basic-webserver/platform/InternalDateTime.roc

Line 9 in d592b4e

 DateTime : { year : I128, month : I128, day : I128, hours : I128, minutes : I128, seconds : I128 } 

This feels exceptionally large for no reason. We should analyze what is required and minimize the waste here.