Remove dependency on `uuid`

Currently `uuid` is used for a random unique identifier for [`ValidatorFn`](https://docs.rs/form-validation/latest/form_validation/struct.ValidatorFn.html) for the `PartialEq` and `Debug` implementations. Perhaps a function pointer could be used instead.

Start with the ValidatorFn entry point and inspect how uuid currently provides the identifier used by its PartialEq and Debug implementations. Determine whether the suggested function-pointer approach can replace that dependency, then verify that both implementations retain their intended behavior and that uuid is no longer required.

Written by the indexing model from the issue text.