Turn off hpc checkpoint saving in SLURM environment if trainer.fit(..., ckpt_path="last")

### Description & Motivation

Hi all,
`trainer.fit(ckpt_path="last")` works perfectly now (in SLURM environment with autorequeue=True), especially if you set up end-of-epoch checkpoint callback. However, the trainer still saves middle-of-the-epoch checkpoints that remain unused because of `trainer.fit(ckpt_path="last")`. It would be great to not save hpc_ckpt if trainer.fit(ckpt_path="last").

This feature will close #13773

### Pitch

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### Alternatives

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### Additional context

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cc @lantiga @borda

Start at the trainer.fit(..., ckpt_path="last") entry point and trace how SLURM autorequeue mode handles middle-of-epoch HPC checkpoints. Determine where the checkpoint-saving decision is made; done means hpc_ckpt is not saved for this mode while existing resume behavior remains intact.

Written by the indexing model from the issue text.