Add stats progress in log and in JSON file for Zimfarm

[benoit74]

Fix #37

Changes:

• report progress in JSON file (for Zimfarm) and log (so that when --debug is not passed, we have visual feedback that scraper is still progressing)
• enrich some logs to display count of items to process, since we need to count them anyway

Remarks: we add 1 more items to process so that progress is not 100% at the beginning when we do not yet know how many items we have to process and so that we can increase counter at the beginning of every for loop, not minding about what could happen in the loop in terms of exit conditions

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 9.37500% with 29 lines in your changes missing coverage. Please review.

Project coverage is 40.54%. Comparing base (c2a6444) to head (a55f69b). Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
scraper/src/mindtouch2zim/processor.py	9.67%	28 Missing :warning:
scraper/src/mindtouch2zim/entrypoint.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #40 +/- ## ========================================== - Coverage 42.21% 40.54% -1.67% ========================================== Files 8 8 Lines 552 582 +30 Branches 69 70 +1 ========================================== + Hits 233 236 +3 - Misses 317 344 +27 Partials 2 2 ```

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