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

CHANGELOG.md

@@ -10,6 +10,9 @@ SPDX-License-Identifier: GPL-3.0-or-later
 [List of commits](https://git.ufz.de/rdm-software/saqc/-/compare/v2.2.1...develop)
 ### Added
 ### Changed
+- Remove all flag value restrictions from the default flagging scheme `FloatTranslator` 
+- Renamed `TranslationScheme.forward` to `TranslationScheme.toInternal` 
+- Renamed `TranslationScheme.backward` to `TranslationScheme.toExternal` 
 ### Removed
 ### Fixed