feat: add reduceKeys function

[aleclarson]

Tip

The owner of this PR can publish a preview release by commenting /publish in this PR. Afterwards, anyone can try it out by running pnpm add radashi@pr<PR_NUMBER>.

Description

Introduce the reduceKeys function which is like Array::reduce but for an object's own keys (i.e. not inherited). It uses the new filterKey function to support either an array of specific keys to reduce or a filter function for more advanced cases.

The basic function signature (minus the generics) is this:

function reduceKeys(
  obj: object,
  filter: KeyFilter,
  reducer: (
    acc: any,
    value: any,
    key: string | number | symbol,
    obj: object
  ) => any,
  initial?: any
): any

In a single loop, it calls the reducer for every key that matches the filter.

When filter is an array of property names, it's used instead of Object.keys for enumeration purposes.

Checklist

• Changes are covered by tests if behavior has been changed or added
• Tests have 100% coverage
• If code changes were made, the documentation (in the /docs directory) has been updated

Resolves