Bump to 4.0.0a1

[ischoegl]

Changes proposed in this pull request

• Bump version to 4.0.0a1 due to pending major version jump (see breaking changes in Simplify Reactor evaluation/synchronization logic #2069, ImproveReactorSurface handling and reimplement advanceCoverages #2075, Introduce std::span usage in thermo classes #2077 and Considerations for next major version (Cantera 4.0) enhancements#250)
• Update copyright version

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• No generative AI was used. This contribution was written entirely without AI assistance.

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
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• AI Statement is included
• The pull request is ready for review

[speth]

There are a handful of references in the documentation to "Cantera 3.3" documenting changes in behavior that should also be updated.

Also, cti2yaml.py needs to be updated as well -- it looks like I messed up the version there as part of the previous bump to 3.3.0a1.

[ischoegl]

There are a handful of references in the documentation to "Cantera 3.3" documenting changes in behavior that should also be updated.

Also, cti2yaml.py needs to be updated as well -- it looks like I messed up the version there as part of the previous bump to 3.3.0a1.

Thanks - I believe I tracked them all down!