Compress images with oxipng

[hugovk]

Fixes #1518.

See #1514 (comment) for amount of compression.

Also add pre-commit hook, and update README about how to use prek, which is a faster version pre-commit client. And you can use either locally.

---

I've not committed the compressed files here, let's see if pre-commit.ci will do it.

[europython-society]

Preview available

Key	Value
url	https://oxipng.ep-preview.click
last update	2026-01-23T11:52:48.850Z

[hugovk]

Hmm, timeout after 180 seconds!

I'll run it locally and push, and see if that makes a difference. Another option is to remove -o=max which should make it quicker, but still compress well.

[hugovk]

Same thing. Let's try without -o=max, locally that speeds it from 2m42s to 11s!

The commit with compression did use -o=max.

[hugovk]

Bingo!