Use loading=lazy on images

[simonw]

https://developer.mozilla.org/en-US/docs/Web/Performance/Lazy_loading

This could help avoid loading a hundred images on a page with a table that doesn't ever get scrolled.

[simonw]

Had this idea while looking at https://til.simonwillison.net/tils/til and thinking about maybe adding this plugin to that.

[simonw]

This idea doesn't actually make sense given the way this plugin works at the moment - it embeds base64 images directly into the page, which results in a BIG increase in the size of the output HTML and no opportunities for lazy loading:

datasette-render-images/datasette_render_images.py

Lines 26 to 30 in e91ee84

	return Markup(
	'<img src="data:image/{};base64,{}" alt="">'.format(
	image_type, base64.b64encode(value).decode("utf8")
	)
	)

[simonw]

In order to add lazy loading I'd need to change how the images are served, switching to having them link to a new endpoint (or output renderer) which returns the image read from the database table.

I'd need to think carefully about the security of doing this, since serving content from potentially untrusted sources could result in XSS or similar if not done with care.