Fix bitmap glyph positioning with scaled transforms

[devunt]

When draw_glyphs() receives a scaled transform (e.g., Affine::scale(2.0)), bitmap glyphs (emoji) render at incorrect positions because:

1. Glyph position offset was scaled by the transform via pre_translate
2. But image_scale_factor and font_units_to_size only used unscaled font_size

This caused a position/size mismatch where bitmap glyphs appeared offset from their expected locations, with the error proportional to the scale factor.

Fix

• Extract scale factor from transform using determinant().abs().sqrt()
• Compute glyph position in physical coordinates before applying to transform
• Use scaled font size for image_scale_factor and font_units_to_size calculations

Screenshots