Fix multiple sessions in one kernel bug

[rakhmaevao]

I found the following error

How to reproduce the bug?

1. Run jupyverse jupyterlab
2. Create a session for the kernel. The kernel itself will start and a session will be created for it.
3. Add another session to the running kernel.

Expected behavior

The session will be added

Actual behavior

Error (see below).

Screencast.from.2024-12-11.15-04-34.mp4

  File "/home/rakhmaevao/Projects/jupyverse/plugins/kernels/fps_kernels/routes.py", line 187, in create_session
    connection_file=self.kernel_id_to_connection_file[kernel_id],
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
KeyError: '68527f9d-7362-4c0a-ac66-d9e429a78246'

How did I fix it?

1. After creating a new kernel (see step 2 of the instructions for reproducing the bug), I added the path to CONNFILE to the mapping. This allowed me to find the path to this file when starting a new session.
2. Additionally, I fixed the kernel restart when another session is created for it. The problem was that when creating an additional session, the KS was rewritten without kernelspec_path. I deleted this rewriting.

Confirmation of functionality

Screencast.from.2024-12-11.15-07-36.mp4

[rakhmaevao]

It seems the tests are already broken. Will we be able to merge my PR or do I need to fix the tests?

@davidbrochart