improve docs again

[veenstrajelmer]

• embed measurements notebook in docs
• clean notebooks/examples (and readme), eg replace netcdf example with ds = df_simple.to_xarray(); ds = ds.assign_attrs(ds_simple.attrs); ds.to_netcdf("file-name.nc") and maybe some variable renaming. Also simplify parallel example so it does not use a nonexising file
• add notebooks to docs/pages
• increase cli test coverage
• fix rwsddl testcase in 794 add slev retrieval from ddl dfm_tools#796
• check timezone example code if all still aligns: Add support for different timezones #40 (we get "Geen gevevens gevonden" at 11-3-2024, this was not the case before) >> also for ddlpy testbank, this is because ddl is currently being updated and much data was temporarily removed. Wait until it is restored.
• change above tests to dummy data, so they will always keep passing also if data is fixed

Follow-up: #79