feat(contracts): DRY refactoring of availableExpectations versus predefinedExpectations

[guzmud]

Backstory

The implementation for availableExpectations and predefinedExpectations defined in #304 , mirroring the implementation from OpenAEV-Platform/openaev#5148 and OpenAEV-Platform/openaev#5554, leads to maintaining two lists in each injectors that need to be synchronized (although the content will vary depending on the wanted user-experience).

This goes against the DRY principle and leads to an eventual desynchronisation between the two lists. Merging both variable to create a single availableExpectations list with a predefined flag per Expectation will provide the same feature while reducing the risk of desynchronisation and minimizing the codebase.

Current workaround

Maintain two fields in pyoaev for two lists inside each injectors.

Proposed solution

Add a predefined field to the Expectation object and merge both lists into a single one.

Edit (2026-17-07)

Expectation needs to be updated with two new booleans:

• expectation_is_predefined
• expectation_is_multi-selectable