Add MultipartFileRecreatable.fromBytes + plugin improvements

[Zazo032]

Fixes #27

6.0.0

• Updated internal libraries.
• Bumped minimum Dart SDK to 3.0.
• Added MultipartFileRecreatable documentation.
• Refactors static constructors to factories.
• Adds a new MultipartFileRecreatable.fromBytes factory compatible with web.
• Added a new headers parameter.
• You can now read the file's content with MultipartFileRecreatable.data.
• Breaking: MultipartFileRecreatable.filename is now a named parameter to match dio.
• Breaking: Removed MultipartFileRecreatable.filePath since it was not being used internally.

[Zazo032]

@rodion-m I noticed running flutter test doesn't run all the tests in the repo because the file's are not using the proper format (<test>_test.dart), it should be fixed in a different PR

[Zazo032]

@rodion-m do you think this could get reviewed anytime soon? We've been using it in production for a couple months now

[rodion-m]

do you think this could get reviewed anytime soon? We've been using it in production for a couple months now

Hello! Sorry for the delay, I was too busy at work. You did a great job, thank you for this. Since your PR makes breaking changes, could you please add information in the README about moving from version 5.0 to 5.1?

[Zazo032]

@rodion-m done 🙂

[rodion-m]

LGTM. Thanks a lot for your contribution!