feat: consider decorating parent class methods with @abstractmethod

[martintb]

We should consider whether our abstract classes, which are used to define API interfaces, should be made to be strict. By using the @AbstractMethod decorator from the abc module of the standard library, you can force derived classes to implement a defined interface.

For example, if we want loading.SyringePump.SyringePump to always have a withdraw and dispense:

from abc import ABC, abstractmethod

class SyringePump(ABC):

     def stop(self):
        raise NotImplementedError

    @abstractmethod    
    def withdraw(self,volume,block=True):
        pass

    @abstractmethod
    def dispense(self,volume,block=True):
        pass
        
    def setRate(self,rate):
        raise NotImplementedError

    def getRate(self,rate):
        raise NotImplementedError

    def emptySyringe(self):
        raise NotImplementedError

See here for a discussion on abstract classes including why they're sometimes better than the NotImplementedError method we currently use.