Migrate `@pure` annotations

[Aclrian]

Is your feature request related to a problem?

After changes to an API, we still want to use most of the @pure annotations.

Desired solution

Migrate the @pure annotations from apiv1 elements to apiv2 elements that are mapped together. If a mapped apiv2 element is a function and has no side effects and whose return value is the same if the parameters passed in the calls are the same, create a @pure annotation for that element.
Otherwise, mark the api element with a @todo annotation, or do not migrate the annotation if the mapped function is not pure.

Possible alternatives (optional)

No response

Screenshots (optional)

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Additional Context (optional)

The code attribute of functions should be useful.

Create the file package_parser/processing/migration/annotations/_migrate_pure_annotation.py with a function to migrate an annotation with the related mapping.
See Safe-DS/API-Editor#1151 for an example of how to migrate annotations.