New allow-duplicates prop for autocomplete, dropdown and taglist pro inputs

[fabiobulgarella]

Summary:
Introduce a new allow-duplicates prop to the FormKit Pro autocomplete, dropdown, and taglist inputs. This optional boolean property would enable developers to control whether duplicate selections are permitted in these components.

Use Case:
Currently, these inputs enforce unique values, which is ideal for many scenarios. However, in cases where repeated selections are meaningful (e.g., tagging duplicate items or selecting identical options for separate purposes), this restriction can limit functionality. Adding allow-duplicates would provide greater flexibility and align with diverse application requirements.

Proposed Behavior:
When allow-duplicates is false (default), duplicate values are not permitted, maintaining current behavior.
When allow-duplicates is true, users can select or add duplicate values without restriction; in this case check marks should not be shown on the selection list.

Benefits:
Enhances component flexibility for broader use cases.
Maintains backward compatibility by defaulting to the existing behavior.
This feature would empower developers to better meet the needs of their applications while preserving the simplicity and reliability of FormKit Pro inputs.