Refactoring: create get_used_port_clocks attribute instead of _extract_port_clocks_used

Explanation of changes

_extract_port_clocks_used(Operation|Schedule) has been moved to Operation.get_used_port_clocks() and ScheduleBase.get_used_port_clocks().
In the future it still needs to be moved to subclasses when wet get rid of is_pulse and is_acquisition.

Motivation of changes

It was a private method used publicly.
It was in a util/helpers class when it could live much more nicely in a the Operation/Schedule classes. Hopefully reduces the amount of circular imports by having less imports in a util/helpers class.

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• 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).
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• Check whether performance is significantly affected by looking at the Performance metrics results.
• Windows tests in CI pipeline pass (manually triggered by maintainers before merging).
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