Overwriting redirects with an item is no longer allowed

[veloman-yunkan]

Fixes #1071

The PR mostly consists of new unit-tests demonstrating how attempts to overwrite existing entries work. Various combinations of the types of the existing entry and the entry being added are tested. The last commit eliminates the deliberate possibility of overwriting a redirection entry with an item entry, updating the unit tests correspondingly.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 56.48%. Comparing base (f730b85) to head (9374cb4).
⚠️ Report is 110 commits behind head on main.

Files with missing lines	Patch %	Lines
src/writer/creator.cpp	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1072      +/-   ##
==========================================
+ Coverage   56.42%   56.48%   +0.06%     
==========================================
  Files         101      101              
  Lines        5069     5065       -4     
  Branches     2211     2208       -3     
==========================================
+ Hits         2860     2861       +1     
+ Misses        741      737       -4     
+ Partials     1468     1467       -1     

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[kelson42]

@veloman-yunkan How does the libzim behaves if we try to overwrite an item?

I thought we should get rid of ASSERT!? #723

[veloman-yunkan]

@veloman-yunkan How does the libzim behaves if we try to overwrite an item?

A zim::InvalidEntry exception is thrown.

I thought we should get rid of ASSERT!? #723

How does it apply to this PR?