Translation cleanups

A number of cleanups and disentanglements to the current translator implementations:

• Extract a real abstract Translator interface
• Remove the mapping based approach from the FloatTranslator to make it actually accept floating point values unequal exact integers

saqc/core/translation/basescheme.py

@@ -30,7 +30,7 @@ class TranslationScheme:  # pragma: no cover
         pass
 
     @abstractmethod
-    def __call__(self, ExternalFlag) -> float:
+    def __call__(self, flag: ExternalFlag) -> float:
         pass
 
     @abstractmethod