Update dependencies: image, base64, sdl2

[sciguy16]

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PR description

Hi, I noticed that the version of image this crate depends on in the published release is 0.23.4 (can be seen on the crates.io page rather than the 0.24.7 promised by the changelog. In the meantime, of course, there's been another version out so I've bumped the 3 now outdated dependencies to their latest versions.

I've also fixed some clippy warnings - let me know if you'd prefer that commit to be moved to a separate PR or if it's okay bundled in with this one.

[sciguy16]

Ah, CI is failing because the bitstream-io transitive dependency of image has an MSRV of 1.79. Might have to back out the image update if we want it to build on 1.71

[rfuest]

Good catch, I don't know how the release version did get out of sync with the repo, but it seems that the release on crates.io is based on d11431f and not the latest commit at that time.

Ah, CI is failing because the bitstream-io transitive dependency of image has an MSRV of 1.79. Might have to back out the image update if we want it to build on 1.71

I wouldn't mind bumping the MSRV a bit, but I think we should at least support a couple of stable releases back if possible.

According to this issue the bump in the MSRV is caused by the ravif feature, which we don't use. By changing the image dependency we might be able to work around the issue:

image = { version = "0.25.1", default_features = false, features = ["png"] }

[sciguy16]

Good spot, I've turned off the default features on image and now the tests pass on 1.71

[rfuest]

LGTM