GitLab

- Introduce generic Operator interface for Optimiser operators.
I will use it more in following PR-s related to #608 to make logic and abstraction of evo algo clear & reusable.

- Current PR introduces only one specfic Evaluate operator.
It keeps everything related to evaluation in one place.
No new logic is added, mostly cleanup and reorganization of the code.

- Also refined type signatures of Graph adapters and added no-op behavior
for already adapted graphs (to avoid excessive checks a-la `adapt if not already adapted)

- Refactor a bit ComposerBuilder to avoid late-initialisation through assignment of composer.optimiser