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

@@ -148,7 +148,7 @@ class MappingScheme(TranslationScheme):
             if flag not in self._backward:
                 raise ValueError(f"invalid flag: {flag}")
             return float(flag)
-        return self._forward[flag]
+        return float(self._forward[flag])
 
     def forward(self, flags: pd.DataFrame | DictOfSeries | pd.Series) -> Flags:
         """