⬆️🐍 Adopt nanobind 3 split-mode wheels

[renovate]

🤖 AI text below 🤖

Description

This PR upgrades MQT Core to nanobind 3 and uses split mode to reduce the release matrix:

• require Python 3.11 or newer;
• publish one cp311-abi3 wheel for GIL-enabled CPython 3.11 and newer;
• publish one cp315-abi3t wheel for free-threaded CPython 3.15 and newer;
• stop publishing CPython 3.13t and 3.14t wheels;
• install nanobind-backend as the required runtime backend;
• require CMake 4.4.1 or newer for Python package builds;
• use nanobind split mode for every Python binding build;
• remove one dense allocation and copy from VectorDD.get_vector();
• protect shared DD, IR, and QDMI state exposed by free-threaded Python.

The branch retains Daniel Haag's original nanobind 3 commits and signed cherry-picks of the Python 3.11 work from #2009.

The QDMI synchronization is isolated in one commit. If #1901 lands first, that commit can be dropped because #1901 removes the legacy driver.

Generated installation and tooling pages come from the MQT templates repository and still need a template-side follow-up.

Validation

• release build
• 4,143 CTest cases passed; one contract-defined skip
• 727 Python tests passed; three expected skips
• final DD vector and matrix suites: 18 passed
• QDMI driver suite: 95 passed
• symbolic concurrency suite: 20 passed
• final cp311-abi3 and cp315-abi3t wheel builds and clean-environment import/DD ownership smoke tests
• strict abi3audit for the classic wheel
• check-wheel-contents for both wheels
• nanobind's split-mode CPython 3.15t suite: 457 passed, 243 skipped
• stub generation
• uvx nox -s lint
• uv lock --check
• git diff --check
• direct split-mode configuration with CMake 3.24 and 4.4
• final cp311-abi3 wheel build with scikit-build-core selecting CMake 4.4.2
• resolved cibuildwheel options preserve full Windows AMD64 tests through CPython 3.14 and smoke-test Windows ARM64 and CPython 3.15
• pre-review hosted CI: 24 of 24 jobs passed across Linux x86-64/ARM64, macOS Intel/ARM64, and Windows x64/ARM64
• pre-review hosted Slurm integration passed
• hosted wheel jobs produced the exact cp311-abi3 and cp315-abi3t artifacts and installed nanobind-backend on all release platforms
• macOS artifact inspection confirmed that ARM modules export only their initializer and Intel modules add only nanobind's four required weak exception RTTI symbols

ThreadSanitizer cannot start on this ARM64 host because its runtime reports FATAL: ThreadSanitizer: unexpected memory mapping. Native concurrency tests and a GIL-disabled CPython 3.15 smoke test cover the new synchronization on this host.

Checklist

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
• I have added entries to the changelog for any noteworthy additions, changes, fixes, or removals.
• I have added migration instructions to the upgrade guide (if needed).
• The changes follow the project's style guidelines and introduce no new warnings.
• The changes are fully tested and pass the CI checks.
• I have reviewed my own code changes.

If PR contains AI-assisted content:

• Any agent that created, edited, or submitted GitHub content was explicitly authorized for that scope, as required by our AI Usage Guidelines.
• Every agent-authored or agent-edited public text body begins with the visible disclosure 🤖 *AI text below* 🤖 (titles are exempt).
• I have disclosed AI assistance in the PR description.
• I confirm that I have personally reviewed and understood all AI-generated content, and accept full responsibility for it.

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/qdmi/driver/Driver.cpp	90.0%	10 Missing ⚠️
include/mqt-core/ir/Register.hpp	50.0%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[burgholzer]

Reviewed all the changes here. This should be pretty close to mergable.

[burgholzer]

This should be ready to go in now! 🙌
Should also help with CI times due to the increased caching. This should imply that the Python tests only build a single instead of three wheels, which should make them much faster.
Same for the CD jobs.