Enhancement: have Trait/HiddenField only there to feed the post_generate of other fields

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### Summary

Hi !

Not sure if Documentation Request or Enhancement, took the second one as I did not found it...

I want to use [Faker's local_latlng](https://faker.readthedocs.io/en/master/providers/faker.providers.geo.html#faker.providers.geo.Provider.local_latlng) to feed several fields, latitude, longitude, city.

I think the way to go is to use post_generate, however now I don't see a better way to do so then to call the function X times and then access the item of the tuple returned by the function by position.

I think it would be cleaner if PolyFactory was supporting some kind of HiddenField (maybe all fields prefixed by `__` ?) to get the value, store the tuple as attribute there, use it to feed other fields, but then never reflect it in model_dump() or other instance logic.

I may have missed a functionality somewhere else...

### Basic Example

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### Drawbacks and Impact

_No response_

### Unresolved questions

_No response_

Start by tracing the post_generate hook and the model_dump behavior referenced in the issue, then inspect how Trait and HiddenField are represented. Define how a hidden value feeds other fields and verify that it is excluded from model_dump() and other instance output while remaining available to dependent generation.

Written by the indexing model from the issue text.