refactor: cleanup related to acquisition redesign

Explanation of changes

This is a code cleanup after !1265 (merged).

• AcquisitionChannelMetadata and AcquisitionMetadata (and related tests) moved from schedules/schedule.py to backends/types/zhinst.py.
• extract_acquisition_metadata_from_schedule and _extract_acquisition_metadata_from_acquisition_protocols (and related tests) moved from helpers/schedule.py to backends/zhinst/helpers.py.
• The Qblox SequencerCompiler._num_acq_per_channel is removed, because now it's unused.

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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 and entry in deprecated code suggestions (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).
• Update Hardware backends documentation if backend interface change or N/A
• 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).
  • Maintainers do not hit Auto-merge, we need to actively check as manual tests do not block pipeline

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For reference, the issues workflow is described in the contribution guidelines.