Remove xFormers enabled warning for block, attention and swiglu

[radek-kucera]

Summary

This PR modifies the logging behavior in the dinov2 model's core modules (SwiGLU, Attention, and Block) to remove/replace the warnings.warn calls about xFormers availability.

Motivation

The existing code raises UserWarnings like:

/home/user/.cache/torch/hub/facebookresearch_dinov2_main/dinov2/layers/swiglu_ffn.py:43: UserWarning: xFormers is available (SwiGLU)
  warnings.warn("xFormers is available (SwiGLU)")
/home/user/.cache/torch/hub/facebookresearch_dinov2_main/dinov2/layers/attention.py:27: UserWarning: xFormers is available (Attention)
  warnings.warn("xFormers is available (Attention)")
/home/user/.cache/torch/hub/facebookresearch_dinov2_main/dinov2/layers/block.py:33: UserWarning: xFormers is available (Block)
  warnings.warn("xFormers is available (Block)")

Since warnings generally indicate potential issues, this can be misleading or distracting to users—especially when everything is functioning correctly.

Benefits

• Reduces unnecessary noise in logs for users who already have xFormers set up.
• Prevents confusion by accurately reflecting the status as an informational message rather than a warning.

Alternative solution

Replace warnings.warn(...) with logging.info(...) to keep the developer awareness that xFormers is being utilized, without implying a problem.

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