Add unit tests examples suite organization

[Jason-Gregoire]

Added 61 unit tests
Added and organized a comprehensive examples directory covering all common accumulate use cases
Refactored code where warranted
Updated/Added readme files

[sigrlami]

Ok,

• everything under .dart_tool is a debris. It's not a part of the source code per se but the execution system
• // on top of the file with the path is debris also
• spaces additions, splitting a single line of code into 2, adding "/" or not adding, in the end, this type of "refactoring" is highly controversial. In other environments will easily lead to "holy war". Good practice to use decisions already made in the repo.
• when working with code, we tried to use the conventional commits practice https://www.conventionalcommits.org/en/v1.0.0-beta.2/ I would suggest using that in the future.

[sigrlami]

LGTM!

You can be the admin, no need to fork and request reviews. Just branch from this repo and self-approve PRs.