Replace impl_pure_record and similar macros with common Python classes

[prehner]

• Removes PyIdentifier, PyChemicalRecord and builds the Python classes directly from the rust versions instead.
• Removes the impl_pure_record, impl_binary_record, and impl_segment_record macros in favor of the new PyPureRecord, PyBinaryRecord and PySegmentRecord that use IndexMap (kwargs) instead of generics
• Splits BinaryRecord<I,M> into BinaryRecord<M> and BinarySegmentRecord. BinarySegmentRecord is (for now) not generic, but rather always using f64 as model record.

No changes to the Rust interface at all. Will break all models that use non-f64 parameters (i.e., bool flags, enums, Vecs (especially with non-fixed lengths)). Therefore, the next step has to be to unify the parameter creation which I think is worth it in terms of maintainability and structure of the Python code.