dflash : clarify output logging of target_layer_ids (#27013)

dflash : clarify output logging of target_layer_ids (#27013)

This commit tries to make the logging of target_layer_ids a bit clearer
and easier to read.

Currently the output generated looks like this:
```console
0.00.468.624 D load_arch_hparams: DFlash extract_layers = [0.00.468.626 D 2, 0.00.468.626 D 6, 0.00.468.626 D 20,
  0.00.468.626 D 30, 0.00.468.627 D 42, 0.00.468.627 D 520.00.468.627 D ]
```
With the changes in the commit the output will be:
```console
0.00.522.765 D load_arch_hparams: DFlash extract_layers = [2, 6, 20, 30, 42, 52]
```