The Polished Website Release

86 pull requests since v5.8.

• 🌐 A new website (#739): tutorials as notebooks that run in the browser, a gallery of the projects with the papers done with them, the publications that use pySDC, and a live SDC/MLSDC demo on the landing page, made possible by an optional numba (#735)
• pySDC on real GPUs: the finite-difference problems and mesh_to_mesh with useGPU (#710, #713, #715, #720, #732), the time-parallel controller across GPUs with NCCL and tutorial step_7 G (#714, #716), and CI on four real GPUs on every push (#707, #717, #730)
• delta-form SDC and MLSDC: sweepers that solve for the correction, and levels that genuinely run in reduced precision (#687, #688, #690)
• docstrings that match the code: every public function and method documented (#744, #746, #747, #756, #758, #763, #764), and the review fixed bugs that silently gave wrong results, e.g. implicit Runge-Kutta on IMEX problems, battery_implicit's source term, the IMEX Runge-Kutta weights and the Rayleigh-Bénard diagnostics (#722, #748–#755, #759–#762, #765–#772)
• tests that can fail: tight tolerances, independent tests, MPI tests under mpi-pytest, and coverage history back in Codecov (#693, #694, #695, #723, #724, #726, #727)
• one Allen-Cahn convention for all Allen-Cahn problems (#691), NumPy 1 and 2 both supported (#686), and controller housekeeping (#677–#683)
• 🤖 how much of pySDC was written with AI help is now declared in aidecl.yaml and checked on every CI run; this time there's no need to smell Claude, it's in the numbers

⚠️ Two changes are not backward compatible, see the changelog.