Update examples to new create_f_cnode

[luisaforozco]

Highlights

• Update 01 and 02 examples to few changes to homogenise the functions used.
• Generated .md and notebook files.
• Add possibility to run all the examples as tests. Sometimes the tests fail unexpectedly, we should create specific tests instead of calling the examples directly.
• Checked also 03.01. Checked all the examples are running, training is not completely fine though.
• Removed all the creation of lhist in examples. This object is created in CoupledNODE but this means that if you run two examples one after each other the same object lhist is going to be used. This is also a problem for other variables because we cannot clear the workspace with a command in between tests (i.e. calls to the examples).

Still can be done in the scope of this PR (?)

• [x] Clean folder coupling_functions
• [ ] ~Remove continuous_make_md.jl, replaced by make_examples.jl~ We keep it.

[SCiarella]

I find continuous_make_md useful to instantly render the latex equations by re-generating the md files, so let's keep that. Maybe we can change the filename and add a small explanation/tutorial later.

Once we remove the coupling_functions I would merge this PR