chore(main): release 8.0.0

[flixopt-release-bot]

🤖 I have created a release beep boop

8.0.0 (2026-07-22)

⚠ BREAKING CHANGES

• ONLY FOR PERSISTE CLUSTERING FILES: the serialized clustering format changed - slice dims are now stored as 'period' (was '_period') plus a new 'dim_names' key. Clustering artifacts saved to JSON/netCDF by an older flixopt no longer load for apply_clustering()/expand() in this version; re-run transform.cluster() to regenerate them. Fresh clustering and same-version round-trips are unaffected. Also raises the minimum tsam_xarray to 0.6.4.

Code Refactoring

• drop clustering dim-rename layer via tsam-xarray DimNames (#739) (cc56774)

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