enable selecting test folder when using nbresult in notebooks

[brunolajoie]

The following PR updates nbresult (without breaking it)

Before

Previously, we could only use nbresult in notebooks at the root

After

Now, we can specify in which subdir folder to store the pickle and where to read the pickle and the test_xxx.py

Demo repo as per screenshot here

Why need this ?

This can be useful for taxifare-model project, where we regroup all tests of the week in the ./tests with 1 subdir per challenge, some test launched from notebooks in ./notebooks, while some other are launched from Makefile and targetting python code located in ./taxifare_model/ml_logic for instance

[brunolajoie]

• What do you think about the idea @krokrob ? (before diving into the code)

[krokrob]

What does the make command returns (before diving into the code) ? cc @brunolajoie

[brunolajoie]

Actually, Make works as well!

[brunolajoie]

• comments fixed ✅
• tested again on nnresultdemo ✅

kev feel free to merge

[brunolajoie]

@gmanchon let's merge?

[krokrob]

AWESOME @brunolajoie