github workflows: add coveralls for test coverage reports

[sloorush]

• closes Test coverage #243

what it does

Add goveralls that gives reports on test coverage of the project.

how it does

Currently covering package accumulator.

It gives reports like this(below) on https://coveralls.io/

## Need suggestion on
Is there a better way to structure the workflows? Because right now, it runs the unit tests twice, which is not ideal or some way the job doesn't run out of memory.

edit: I found the issue of the Job getting cancelled, working on it
edit: work done

[sloorush]

Ready for review!

@kcalvinalvin @adiabat Please take a look at it 😄

[kcalvinalvin]

Most of the code is the same right? It's a bit hard to review since there's removed lines that turn this into a decently sized change. Could you add those back in to minimize the lines of change?

[sloorush]

Most of the code is the same right? It's a bit hard to review since there's removed lines that turn this into a decently sized change. Could you add those back in to minimize the lines of change?

YAML formatter suggested moving the steps by one indent ahead, so they were indented automatically
Shifted them back to the previous indent! 😄

[kcalvinalvin]

Tested. Looks good 👍

[sloorush]

@adiabat @kcalvinalvin, this PR can be merged. 😅

[kcalvinalvin]

@adiabat @kcalvinalvin, this PR can be merged. 😅

I don't have merge access to this repo. @adiabat?