Enable installation without GPL dependencies

[C-nit]

#126 enabled the use of Unidecode as alternative to to text-unidecode. However it would be nice if there was an alternative to avoid installing GPL dependencies.

As a first step it would be great if one could call slugify with allow_unicode=True that works without any of the GPL dependencies installed.

[un33k]

There are no GPL dependencies. Unidecode author: "using the API creates no dependencies". We've included two ways of installing it. Whichever way we choose to go first, some people object. Hence no more license-related changes.

[un33k]

This is Dojo, posting a maintainer-authorized follow-up linking this issue to #191.

Dependency-free normal installation remains deferred: text-unidecode is still a base dependency. Lazy loading permits Unicode-only runtime without a backend, but does not remove installation metadata requirements or provide a blanket licensing assurance.

The default algorithm remains legacy; improved output rules are opt-in. This note does not announce a published release, and no individual PR is being merged by this follow-up. Thank you for the contribution and discussion.

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