Run all image decoding through a central place

.github/workflows/main.yml

Dockerfile

api/unstable/info.go

cmd/plugin_antispam_ocr/main.go

go.mod

go.sum

pipelines/_steps/upload/blurhash_async.go

test/test_internals/util.go

thumbnailing/i/heif.go

thumbnailing/i/jpg.go

thumbnailing/i/mp3.go

thumbnailing/i/png.go

util/idec/decode.go