use preliz under the hood of `find_constrained_prior`

[aloctavodia]

In https://github.com/pymc-devs/pymc/pull/7680#issuecomment-2709633765 it was suggested that instead of deprecating find_constrained_prior, we should call PreliZ's maxent function.

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📚 Documentation preview 📚: https://pymc--7905.org.readthedocs.build/en/7905/