feat: upgrade to grumbler scripts 8

[dtjones404]

DTPPSDK-954

• Migrated to grumbler scripts v8.
• Added flow-typed, jest, and cross-env as explicit dev-dependencies.
• Added declaration for DEBUG to resolve flow error
• Removed /test/eslintrc

[codecov-commenter]

Codecov Report

Base: 73.31% // Head: 73.31% // No change to project coverage :thumbsup:

Coverage data is based on head (de69edd) compared to base (3def815). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #112 +/- ## ======================================= Coverage 73.31% 73.31% ======================================= Files 26 26 Lines 952 952 ======================================= Hits 698 698 Misses 254 254 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=krakenjs). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=krakenjs)

:umbrella: View full report at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.