Fix Windows font selection in smoke tests

[Saket7002]

Summary

Fixes #106.

The smoke-test PDF helper used a Linux-only DejaVu Sans path:

/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf

On Windows, that path does not exist, causing the test helper to fall back to Helvetica, which cannot reliably render Greek Unicode text.

This change:

• keeps the existing DejaVu Sans path for Linux
• adds the Windows system Arial font as a fallback
• uses the discovered Unicode-capable font for both PIL and FPDF
• removes the deprecated uni=True FPDF usage
• keeps the change limited to tests/test_pipeline_smoke.py

Testing

• git diff --check passes
• Verified the font helper selects C:\Windows\Fonts\arial.ttf on Windows
• Verified the patched _write_pdf() helper successfully generates a PDF containing Greek text (Καλημέρα κόσμε)
• The full smoke-test module could not be executed because docling and glossapi_rs_cleaner are not installed in the local environment

[DrDimitriosChionis]

I tested this PR on the Windows 10 environment where #106 was originally reproduced.

Environment:

• Python 3.11.9
• PyTorch 2.5.1+cu121
• CUDA available on NVIDIA GeForce GTX 960M
• docling and both Rust extensions installed

With PR #107 checked out, the original FPDF Unicode/Helvetica failures are gone. The full smoke-test module now gets further and reports 2 passed, 1 failed, 1 skipped instead of the original 1 passed, 2 failed, 1 skipped.

The remaining failure is in test_docling_math_pipeline_with_mixed_pdfs at:

assert greek_row["greek_badness_score"] > 60
E assert 55.556 > 60

That looks separate from the font-selection bug. I also tried Segoe UI Symbol (seguisym.ttf) locally because Arial warns that it is missing the subscript-zero glyph. Segoe UI Symbol removes that missing-glyph warning, but the greek_badness_score remains exactly 55.556, so changing the Windows fallback font does not resolve the remaining assertion.

So from my Windows reproduction, this PR does fix the original issue #106, while exposing a separate environment-sensitive smoke-test failure further downstream.