Refactor: Simplify computation of checksum and words

[Tabaie]

This PR integrates the process of breaking up the input into words and computing the checksum into one out-of-snark function.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How has this been tested?

In e2e_test.go a few new tests for the integrated words/checksum function have been added.

How has this been benchmarked?

Not benchmarked.

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[gbotrel]

@Tabaie I assume this PR is outdated and we can close ?