Z3ST: An open-source FEniCSx framework for thermo-mechanical analysis

Fixes the package metadata, which was invalid in 0.3.1. The SPDX license expression under PEP 639 requires setuptools 77 or later, while the build requirement still allowed 64, so building without isolation failed with "invalid pyproject.toml config: project.license". Anyone installing 0.3.1 with --no-build-isolation hit this. The build requirement is now correct, and LICENSE.txt and NOTICE are declared through license-files, so both ship inside the wheel. Clarifies the licensing terms. The NOTICE file previously asked for proper credit as a condition of use, which Apache 2.0 does not impose and which made the terms ambiguous on inspection. Citation is now stated as a request following scholarly practice, pointing at CITATION.cff, and separated from the license conditions. The copyright line reads 2025-2026 Giovanni Zullo, Politecnico di Milano across NOTICE, LICENSE.txt and the documentation. No changes to the physics, the models or the case results. The verification and regression suites are unaffected.