kv-cache : skip alignment of n_stream in kv-cache log msg [no ci] (#15040)

kv-cache : skip alignment of n_stream in kv-cache log msg [no ci] (#15040)

This commit removes the right alignment the `n_stream` value in the
log message in the `llama_kv_cache_unified` constructor.

The motivation for this change is to enhance the readability of log
message. Currently the output looks like this:
```console
llama_kv_cache_unified: size = 2048.00 MiB (  4096 cells,  32 layers,  1/ 1 seqs), K (f16): 1024.00 MiB, V (f16): 1024.00 MiB
```
Notice that the `n_stream` value is right aligned, which makes it a
little harder to read.

With the change in this commit the output will look like
```console
llama_kv_cache_unified: size = 2048.00 MiB (  4096 cells,  32 layers, 1/1 seqs), K (f16): 1024.00 MiB, V (f16): 1024.00 MiB
```