chore: replace `.npmignore` with `files` field

[jonkoops]

What kind of change does this PR introduce?

• [ ] Bug Fix
• [ ] Feature
• [ ] Refactoring
• [ ] Style
• [ ] Build
• [x] Chore
• [ ] Documentation
• [ ] CI

Did you add tests for your changes?

• [ ] Yes, my code is well tested
• [x] Not relevant

If relevant, did you update the documentation?

• [ ] Yes, I've updated the documentation
• [x] Not relevant

Summary I've removed the .npmignore file as the files field in the package is enough for NPM to determine which files should be included. To see this in action run npm pack --dry-run in the root directory.

Does this PR introduce a breaking change? No.

Other information None.

[github-actions[bot]]

:tada: This PR is included in version 0.7.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: