Add regression test for SVG length unit conversion

[rursache]

Summary

• Adds a test verifying SVG root width/height attributes with units (cm, in) are correctly converted to pixels
• The unit conversion was already implemented (10cm → 377px, 2in → 192px) but lacked a specific test for SVG root element parsing

Test plan

• Added svgWithUnits() test verifying width="10cm" → 377 and height="2in" → 192
• All 194 tests pass

Relates to #42

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.42%. Comparing base (6238058) to head (6305b70).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #121      +/-   ##
==========================================
+ Coverage   89.02%   89.42%   +0.40%     
==========================================
  Files         159      159              
  Lines       11959    15399    +3440     
==========================================
+ Hits        10646    13770    +3124     
- Misses       1313     1629     +316     

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