Fix return type on group function

[sodiray]

Description

The group function should return a partial of TKey because it's possible the object does not include all possible TKey keys.

To illustrate:

const groups = group(list, match)

// typeof groups['not-here'] is []
console.log(groups['not-here']) // is undefined

Wrapped return type in a Partial to fix 👍

Checklist

• Changes are covered by tests if behavior has been changed or added
• Tests have 100% coverage
• If code changes were made, the version in package.json has been bumped (matching semver)
• If code changes were made, the yarn build command has been run and to update the cdn directory

Resolves

n/a

[sodiray]

Unfortunately, even though this is just a small type change it is a breaking one for the typescript users. You can see how I had to update the tests. This will stay pending until we have enough to reason a v10 release.