Also take padding into account for centered alignment, necessary since
our constraint type allows asymmetric padding.

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.

We don't really have any large outstanding regressions on -ng to warrant
keeping this alive anymore. ¡Adiós!

We now also have absolute perfect control over the raster position under
FreeType as well. This means that, for example, powerline extended chars
are appropriately clamped to the cell edges at all sizes.

This should be purely an improvement over what we had before, and now it
also matches what we do for CoreText.