docs: add schema example for encrypted data-frames

[RomanBredehoft]

refs https://github.com/zama-ai/concrete-ml-internal/issues/4376

[github-actions]

⚠️ Known flaky tests have been rerun ⚠️

One or several tests initially failed but were identified as known flaky. tests. Therefore, they have been rerun and passed. See below for more details.

Failed tests details

Known flaky tests that initially failed:

• tests/torch/test_brevitas_qat.py::test_brevitas_tinymnist_cnn[True-True-3]

[andrei-stoian-zama]

Great example in the notebook!

For the code in the nb, could you change the

schema = {
    "index": {
        "client_1": 1,
        "client_2": 2,
        "client_3": 3,
        "client_4": 4,

to use a generator to make it shorter?

The notebook text must be changed:

• don't use the first person
• explain limitations and future fixes in a better manner

[github-actions]

Coverage passed ✅

Coverage details

---------- coverage: platform linux, python 3.8.18-final-0 -----------
Name    Stmts   Miss  Cover   Missing
-------------------------------------
TOTAL    7799      0   100%

59 files skipped due to complete coverage.

[andrei-stoian-zama]

Thanks for the changes