python - implement uint8 int8 and float128 support for serialization

[baywet]

related #1287
related #1367

OpenAPI supports additional formats that were not additionally accounted for in the generator. Support for those 3 types (and maybe more if some were missing, see linked PR for examples of types) must be added.

TODO:

• update the parse node interface
• update the serialization writer interface
• update the convention service
• (opt) add required additional imports in the refiner
• update the json parse node implementation
• update the json serialization writer implementation