Add utility function to compute/check ZIM descriptions

[benoit74]

Fix #110

Changes:

• new utility function compute_descriptions in inputs.py to compute ZIM-compliant descriptions based on default and user-provided values
• small improvements to tox configuration
• small type hint fix of handle_user_provided_file in inputs.py

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (4f8c3cc) 100.00% compared to head (591c6dc) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #111 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 32 32 Lines 1302 1319 +17 ========================================= + Hits 1302 1319 +17 ``` | [Files Changed](https://app.codecov.io/gh/openzim/python-scraperlib/pull/111?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim) | Coverage Δ | | |---|---|---| | [src/zimscraperlib/constants.py](https://app.codecov.io/gh/openzim/python-scraperlib/pull/111?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim#diff-c3JjL3ppbXNjcmFwZXJsaWIvY29uc3RhbnRzLnB5) | `100.00% <100.00%> (ø)` | | | [src/zimscraperlib/inputs.py](https://app.codecov.io/gh/openzim/python-scraperlib/pull/111?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim#diff-c3JjL3ppbXNjcmFwZXJsaWIvaW5wdXRzLnB5) | `100.00% <100.00%> (ø)` | | | [src/zimscraperlib/zim/metadata.py](https://app.codecov.io/gh/openzim/python-scraperlib/pull/111?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openzim#diff-c3JjL3ppbXNjcmFwZXJsaWIvemltL21ldGFkYXRhLnB5) | `100.00% <100.00%> (ø)` | |

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[rgaudin]

@benoit74 I had this stashed. Can you review this commit? Also please add your change to CHANGELOG and we'll be good to merge

[benoit74]

It's ok for me, and I've added my CHANGELOG. I let you merge since I can't 😆