Elementary 3.0.0

[Feat!]: Dart 3 support (#86)

* Docs: Update dart docs for core part (partially, WIP).

* Chore: handle Dart 3

* Feat: use interface instead of classes and finalize the elementary(element).

* Feat: ListenableState now is pure interface.

* Docs: update documentation.

* Docs: update documentation.

* Docs: update documentation.

* Docs: update documentation.
Refactor: Entity state, Entity Builder.
Test: adjust test, add a few missed.

* Chore: add changelog for the new version of elementary.

* Chore: add changelog for the new version of elementary_test.

* Chore: update examples to support new version elementary.

* Docs: small cosmetic documentation improvement.

* Feat: add alias for EntityStateNotifier interface.

* Docs: update main page for repository.

* Docs: update main page for repository.

* Refactor: move wrappers, builders and pub-subs into separate package.

* Chore: add workflow for elementary_helper.

* Docs: big update of documentation.

* Chore: update workflows, replace deprecated flutter format.

* Refactor: format code for elementary helper.

* Chore: rename directory to follow pub convention.

* Chore: elementary_test preparation to release.

* Chore: adjust examples.

* Feat: update templates for cli tool.

* Feat: update templates for mason.

* Refactor: fix warnings.

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Co-authored-by: KristinaZoteva <[email protected]>