Checkpointing current_file_id for file insertion

[OGaboriault]

Description

The current_file_id wasn't being checkpointed. This means that the next file being used to insert particles would be the first one after a restart.

Solution

current_file_id is now being checkpointed.

Testing

Havent been tested yet, but I dont think it need to be. Logically, it should work.

Documentation

N/A

Miscellaneous (will be removed when merged)

N/A

Checklist (will be removed when merged)

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Code related list:

• [X] All in-code documentation related to this PR is up to date (Doxygen format)
• [X] Lethe documentation is up to date
• [x] Fix has unit test(s) (preferred) or application test(s)
• [X] The branch is rebased onto master
• [X] Changelog (CHANGELOG.md) is up to date
• [X] Code is indented with indent-all and .prm files (examples and tests) with prm-indent

Pull request related list:

• [X] Labels are applied
• [X] There are at least 2 reviewers (or 1 if small feature) excluding the responsible for the merge
• [X] If this PR closes an issue or is related to a project, it is linked in the "Projects" or "Development" section
• [X] If the fix is temporary, an issue is opened
• [X] The PR description is cleaned and ready for merge

[acdaigneault]

You said no need to test it, but did ou make sure it works? Like, you tried a restart? I know it might be a like specific, but I would add a test. If somehow something else broke that feature, will would be a painfull to debug. Failling restarts are hard to debug as we have seen lately. :) but since it's a tinny PR, maybe let's agree on adding a test later

[blaisb]

I think I agree with @acdaigneault I would prefer if you could add a test here. Does not have to be complicated, but it will be impossible to verify that this feature still works correctly TBH, we have added a lot of restart tests lately, but we need even more

[OGaboriault]

I'll do a test tonight or tomorrow