feat: add new callback hook `on_checkpoint_write_end`#21323

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Iruos8805 wants to merge 7 commits intoLightning-AI:masterfrom

Iruos8805:feature/15795/on-checkpoint-write-end-callback

Commits on Nov 2, 2025

Add on_checkpoint_write_end callback hook and tests
Iruos8805
committed

Commits on Nov 4, 2025

Commits on Nov 9, 2025

Merge branch 'master' into feature/15795/on-checkpoint-write-end-callback
Iruos8805
authored

Commits on Nov 12, 2025

Merge branch 'master' into feature/15795/on-checkpoint-write-end-callback
Iruos8805
authored

Commits on Dec 1, 2025

Merge branch 'master' into feature/15795/on-checkpoint-write-end-callback
Iruos8805
authored