feat: add gate merging pass for Rz gates

Markrequested to merge
feature/rz-gate-merging into main

Explanation of changes

This merge request implements merging of subsequent Rz gates into a single gate with theta being the sum of the merged gate thetas. This would cause an error before.

Motivation of changes

This change is implemented as a simple compiler pass, before timing is done, as operations are possibly changed.

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

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

Edited by Mark

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