Fix: HistologyWash mass field expects an int

[mekhlakapoor]

closes #37

This PR:

• updates the definition of HistologyWashData.mass to expect int not Decimal (the openapi generator serializes Decimal as StrictStr so although Decimal works for the server, it fails validation with client)
• I downloaded all of the histology data from SLIMS to double check the type of the mass field. They were all None or int