Use native Pillow v11.2.0 AVIF format

[Stormheg]

Fixes #166

Pillow v11.2.0 was released today with AVIF support as a notable new feature.

Requires raising the minimum version of Pillow. Only the latest Pillow release receives active support so requiring the latest version doesn't seem like a big issue to me. Especially now that AVIF support in pillow-heif is deprecated, as noted in #166

[Stormheg]

This isn't a valid option when encoding a grayscale image, should be 4:0:0 instead (grayscale is Pillow L or LA mode image) - something for a follow up?

[zerolab]

let's do it as a follow up (as long as you have the time :D)

[Stormheg]

Tried writing a failing test but it turns out save_as_avif will convert from LA to RGBA internally - which makes this not really relevant... or at least not without same yak shaving to figure out why the conversion is happening.

Let's leave this here for now.

[Stormheg]

Marking as draft for now, this needs more work (upstream)

The Pillow 11.2.0 release was retracted because the added AVIF encoders/decorders severely increased the size of prebuilt wheels, causing the project to hit its PyPI upload limit which resulted in not all platforms having a prebuilt 11.2.0 wheel available. As a result, 11.2.1 was released which no longer ships with the libavif library included by default. ¹ Including libavif requires building from source, which is a hassle.

This poses an issue for this PR as we can no longer assume AVIF support is available.

The Pillow maintainers have indicated that they will revisit the issue in 11.3.0, so let's cross our fingers and hope they manage to fix the issue ².

Footnotes

1. https://github.com/python-pillow/Pillow/blob/7a0092f2072a5deca433e2a6b752eced49e4ee16/docs/releasenotes/11.2.1.rst?plain=1#L6-L10 ↩

2. https://github.com/python-pillow/Pillow/pull/8876#issuecomment-2798906089 ↩

[Stormheg]

Closing, superseded by #170