fix: freetype bitmap glyph cast

[GGRei]

Summary

This was exposed by vlang/gui CI when compiling vglyph as a dependency with -W on macOS.

After FT_Glyph_To_Bitmap, the glyph is intentionally reinterpreted as FT_BitmapGlyphRec. V now requires this pointer cast to be explicit unsafe, so this PR marks only that cast as unsafe and leaves the FreeType flow unchanged.

Changes

• Wrap the FT_GlyphRec -> FT_BitmapGlyphRec cast in unsafe.
• Apply vfmt to the touched file.

Context

This was exposed by vlang/gui CI when compiling examples with -W on macOS.

Tests

v fmt -verify -inprocess glyph_atlas.v
git diff --check
v test .