fix(types): correct FuseSortFunctionMatch key type from string to object

[kaigritun]

Problem

The key property in FuseSortFunctionMatch is typed as string, but the actual runtime value is an object created by createKey() in KeyStore.js.

As reported in #811, when using sortFn, the logged key shows:

key: {path: Array(1), id: 'name', weight: 1, src: 'name', getFn: null}

Solution

This PR:

1. Adds a new FuseKey<T> type that correctly represents the key object structure:

   • path: string[] - the path segments
   • id: string - the key identifier (joined path)
   • weight: number - the assigned weight
   • src: string | string[] - the original source key name
   • getFn - optional custom getter function

2. Updates FuseSortFunctionMatch.key to use FuseKey<any> instead of string

3. Updates the JSDoc example to reflect the actual object structure

Testing

All existing tests pass (121 tests).

Fixes #811