fix(font): Improve FreeType glyph measurements and add unit tests for face metrics (#8738)

Follow-up to #8720 adding

* Two improvements to FreeType glyph measurements:
- Ensuring that glyphs are measured with the same hinting as they are
rendered, ref
[#8720#issuecomment-3305408157](https://github.com/ghostty-org/ghostty/pull/8720#issuecomment-3305408157);
- For outline glyphs, using the outline bbox instead of the built-in
metrics, like `renderGlyph()`.
* Basic unit tests for face metrics and their estimators, using the
narrowest and widest fonts from the resource directory, Cozette Vector
and Geist Mono.

---

I also made one unrelated change to `freetype.zig`, replacing
`@alignCast(@ptrCast(...))` with `@ptrCast(@alignCast(...))` on line
173. Autoformatting has been making this change on every save for weeks,
and reverting the hunk before each commit is getting old, so I hope it's
OK that I use this PR to upstream this decree from the formatter.

pkg/freetype/main.zig

@@ -9,6 +9,7 @@ pub const Library = @import("Library.zig");
 
 pub const Error = errors.Error;
 pub const Face = face.Face;
+pub const LoadFlags = face.LoadFlags;
 pub const Tag = tag.Tag;
 pub const mulFix = computations.mulFix;