Allow any callable for adaptive functions and raise TypeError if not valid

Explanation of changes

Small change to the adaptive subroutine.

An instance check that checks if the adaptive_function is indeed a FunctionType is changed to a check if it is callable. Also, A TypeError is raised when the adaptive function is neither a BaseLearner, nor is callable.

Motivation of changes

When using cython-compiled python code (as we do internally), the passed adaptive function (which is a cyfunction instance) does not pass the instance check, since a cyfunction is not a subclass of the FunctionType. This causes the subroutine to pass silently (since no exception is raised when both checks fail).

This change allows for any callable to be passed (also objects that are callable, which potentially allows for a more powerfull interface too). To improve debugging, I've added the TypeError - if it were present, it'd saved me some ours of debugging :)

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Merge checklist

See also merge request guidelines

• Merge request has been reviewed (in-depth by a knowledgeable contributor), and is approved by a project maintainer.
• New code is covered by unit tests (or N/A).
• New code is documented and docstrings use numpydoc format (or N/A).
• New functionality: considered making private instead of extending public API (or N/A).
• Public API changed: added @deprecated (or N/A).
• Newly added/adjusted documentation and docstrings render properly (or N/A).
• Pipeline fix or dependency update: post in #software-for-developers channel to merge main back in or update local packages (or N/A).
• Tested on hardware (or N/A).
• CHANGELOG.md for breaking changes and AUTHORS.md have been updated (or N/A).
• Windows tests in CI pipeline pass (manually triggered by maintainers before merging).
  • Maintainers do not hit Auto-merge, we need to actively check as manual tests do not block pipeline

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