Include missing imports of _operation_representation_types to operations/__init__.py

Notice:
These are the slow ones.

Command:
time python -X importtime schemas/__private/operations/__init__.py

Before:
python -X importtime   0,17s user 0,03s system 99% cpu 0,196 total

After:
python -X importtime   4,47s user 0,09s system 99% cpu 4,560 total