[mazkev]

Describe your changes

In the mutable package, func Fill was accidentally declared inside mutable/slice_example_test.go instead of mutable/slice.go.

Because Go omits _test.go files during compilation for external consumers, mutable.Fill was not actually exported in the public API when importing github.com/samber/lo/mutable (undefined: mutable.Fill).

Changes made:

1. Move func Fill: Moved from mutable/slice_example_test.go to mutable/slice.go.
2. Add ExampleFill: Added a runnable ExampleFill() in mutable/slice_example_test.go to verify the example and keep documentation examples complete.
3. Update Documentation:
   • Updated sourceRef in docs/data/mutable-fill.md to point to mutable/slice.go#L78.
   • Fixed example snippet in docs/data/mutable-fill.md to use lom.Fill instead of lo.Fill.

Verification:

• go doc ./mutable now correctly lists:

  func Fill[T any, Slice ~[]T](collection Slice, initial T)