[CO-354] Make use of an Int32 instead of a Word32 in NetworkMagic

[intricate]

Description

Linked issue

https://iohk.myjetbrains.com/youtrack/issue/CO-354

Type of change

• 🐞 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 change)
• 🏭 Refactoring that does not change existing functionality but does improve things like code readability, structure etc
• 🔨 New or improved tests for existing code
• ⛑ git-flow chore (backport, hotfix, etc)

Developer checklist

• I have read the style guide document, and my code follows the code style of this project.
• If my code deals with exceptions, it follows the guidelines.
• I have updated any documentation accordingly, if needed. Documentation changes can be reflected in opening a PR on cardanodocs.com, amending the inline Haddock comments, any relevant README file or one of the document listed in the docs directory.

Testing checklist

• I have added tests to cover my changes.
• All new and existing tests passed.

QA Steps

Screenshots (if available)

[mhuesch]

LGTM but we should get an external review.