chore: optimize down the public/ dir png files

## Problem

When looking at our cloudflare analytics today it called out a few
images as offenders in our LCP. Our LCP is generally quite "good" with
70% of all requests under 2.5 seconds. But these images were called out
as potential offenders, Im thinking its their weight

Slimming down their weight should help pageload times where these images
appear.

My plan is to watch the LCP stats over the next few weeks to measure
how much of an impact this change had. Specifically for the
/5x/guide/writing-middleware/ page bc that was cited as the worst in a
couple langs like Japanese.

## Solution

This PR optimizes all our pngs in the public/ dir in place.

| File | Before | After | Reduction |
|---|---:|---:|---:|
| `public/apple-touch-icon.png` | 3,557 B | 978 B | 72.5% |
| `public/images/blog/redesign/before-after.png` | 435,879 B | 140,677 B | 67.7% |
| `public/images/blog/redesign/brand-values.png` | 92,724 B | 36,181 B | 61.0% |
| `public/images/blog/redesign/logo-favicon.png` | 47,064 B | 16,418 B | 65.1% |
| `public/images/blog/redesign/vision-mission.png` | 82,218 B | 31,845 B | 61.3% |
| `public/images/clustering.png` | 6,254 B | 3,696 B | 40.9% |
| `public/images/express-mw.png` | 119,397 B | 36,423 B | 69.5% |
| **Total** | **787,093 B** | **266,218 B** | **66.2%** |

I ran all the pngs in the public dir through [pngquant](https://pngquant.org/)

```sh
find public -name '*.png' -exec pngquant --quality 80-98 --skip-if-larger --strip --force --ext .png {} \;
```
in order to "quantize" the pngs. these are simple diagrams/logos mostly
so they are pretty well suited to pngquant optimization.

The `--quality 80-98` makes pngquant refuse to save any image that would
fall below that quality floor. And I spot checked all the images
manually against their previous versions and could see no difference.

### context

Background on this is that anything in our public dir is not part of the
astro build pipeline, so the images will not be optimized into webp like
things in our src dir. This PR's in place optimization lets us see how/if our
web vital stats are impacted by optimizing these images, without having
to update any content pages to point to either new images (swapping png
for webp for example) or a new image location.

We can eventually move images into the src dir if we wish for anything
added in the future to be optimized via the build process, so we dont
have to do maual optimizations like this or think much about it in the
future (there are also some drawbacks to letting astro handle the images for
us, like it lazy loading images in markdown content etc which can
actually hurt LCP).

Author: jonchurch