…ocketPy-Team#852)

* ENH: add time variable density to Tank Fluids.

* TST: add tests for variable fluid density.

* STY: running isort for import order consistency.

* DOC: update Fluid docs with variable density explanations.

* MNT: use Union is Fluid dataclass type for Python <3.10 support.

* ENH: add time variable density to Tank Fluids.

* STY: running isort for import order consistency.

* MNT: use Union is Fluid dataclass type for Python <3.10 support.

* MNT: refactor density variation for temperature and pressure inputs.

* MNT: improve Tank class outputs (WIP).

* DOC: update fluid density documentation.

* MNT: Add CAD data for tank geometry validation.

* MNT: Refactor tank testing and improve file structure.

* MNT: add recent changes to CHANGELOG.

* MNT: post merge fixes from testing refactors.

* MNT: post rebase fixes.

* TST: introduce testing to variable density tanks.

* MNT: Add recent changes to CHANGELOG.

* TST: improve fluid tests and solve review comments.