Feat: DataHandler - allow nested figures and arrays to be saved

[nulinspiratie]

This PR enables the data handler to also save figures and arrays when they are nested within a dict.

Example:

data = {"q1": {"trace": np.array([1, 2, 3]), "fig": plt.figure()}}
data_handler.save_data(data, "my_data")

Afterwards, the data will be stored in: q1.trace.npy and q1.fig.png

[github-actions]

Unit Test Results

389 tests   385 ✔️  44s ⏱️
    1 suites      4 💤
    1 files        0 ❌

Results for commit 9310577.

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