Potentially add back streamed image decoding

[CosmicHorrorDev]

With image's new v0.25 release we'll lose out on the streamed image decoding added in #74 (changes to an upstream trait dropped how we turned the decoder into a reader in order to make it object safe)

It's worth noting that once #291 is finished the non-streamed decoding won't be an issue for images loaded from the global cache since they're stored pre-decoded in the format we already expect. That means any images fetched through urls that are either fresh, or have a valid e-tag won't need to be decoded

There's a few things we can do to mitigate things in various ways with widely varying degrees of difficulty (some of which we really ought to do anyways)

• Limit the amount of large images that we decode simultaneously (have some separate worker pool for it)
• Use the underlying library for some of the most common formats to support streaming (highly non-trivial)
• Realistically we should error out on images that would decode above a specific size anyways (it's based off the image's dimensions, not the file size, so it'll have to be some decently large default limit like 256 MiB or so)