FEAT: use Decimal instead of float

[TheTechRobo]

Is your feature request related to a problem? Please describe.
the well-known decimal bug (0.1 + 0.2 != 0.3). try it out yourself.

This isn't a Palc bug, but using the Decimal class, although it's slower, should mitigate this problem.

This will also require some refactoring on mathmod's side to support not converting to a float.