feat:add parametric melt-quench workflow and docs

[Atilaac]

This PR addresses issue #160.

Introduce a new parametric_melt_quench workflow to run simulations using different system sizes and cooling rates.

• adds amorphouspy/workflows/parametric.py.

• Includes user documentation at docs/theory/workflows/parametric.md and updates mkdocs.yml to include the new theory page and adjust the docs navigation (reordering and commenting a Parametric notebook entry).

• The workflow caches one initial structure per system size and returns a flat list of results for each (n_atoms, cooling_rate) pair.

• I will include a notebook later using pre-simulated data, which I will just read from a JSON file. I can not make the notebook run slow cooling rates or a large number of atoms here.

[codecov]

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[ltalirz]

Thanks a lot @Atilaac - we will indeed need a workflow of this type. There is one more convergence dimension by the way: the number of samples for given size and cooling rate.

We should think carefully about how we want to design this, let's discuss it later

[Atilaac]

I'm not sure this is necessary for this type of benchmarks. The changes with cooling/system size should be way larger than sample to sample fluctuations. I had this in mind yesterday but I decided to not add it because I wouldn't do sample statistics for this type of convergence tests.

PS: it can easily be added.