feat: add support transparency

[mbfakourii]

Add support transparency export (thanks @brendan-duncan in https://github.com/brendan-duncan/image/issues/663). Add support export base maximum frame size (thanks @brendan-duncan in https://github.com/brendan-duncan/image/issues/664). Improve example project base last flutter changes.

Closes: #27 Closes: #39

Pre-launch Checklist

• [x] I made sure the project builds.
• [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• [x] I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy], or this PR is does not need version changes.
• [x] I updated CHANGELOG.md to add a description of the change.
• [ ] I updated/added relevant documentation (doc comments with ///).
• [ ] I rebased onto main.
• [ ] I added new tests to check the change I am making, or this PR does not need tests.
• [ ] I made sure all existing and new tests are passing.
• [x] I ran dart format . and committed any changes.
• [x] I ran flutter analyze and fixed any errors.

[ueman]

I can't release a new version, so that has to be done by Baseflow.

cc @mvanbeusekom @JeroenWeener @TimHoogstrate

[martijn00]

@ueman I'll rework the CI so it supports pushing new releases from there.

[martijn00]

@ueman I've implemented it, fixed some issues and released a new version. You can now make a new release by just setting a new tag. You need to make sure the changelog and version is updated before doing that.