Switch auto field stats to an item pipeline

[Gallaecio]

I was asked to support non-standard, custom items for auto field stats.

To achieve that, it seemed easier to switch the implementation to an item pipeline.

It also feels like this feature would make sense in scrapy-poet now. But I am not 100% sure, and I also would not want to move it until scrapy-poet gained add-on support.

To do:

• Merge and release Prevent None.cast call zytedata/zyte-common-items#102, and update setup.py and tox.ini accordingly.
• Wait for @asadurski to test it out in a real project.

[codecov]

Codecov Report

Attention: Patch coverage is 98.41270% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.85%. Comparing base (106b099) to head (a89f3b7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
scrapy_zyte_api/_poet_item_pipelines.py	98.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #216      +/-   ##
==========================================
+ Coverage   97.67%   97.85%   +0.17%     
==========================================
  Files          14       16       +2     
  Lines        1550     1585      +35     
  Branches      327      333       +6     
==========================================
+ Hits         1514     1551      +37     
+ Misses         15       12       -3     
- Partials       21       22       +1     

Files with missing lines	Coverage Δ
scrapy_zyte_api/addon.py	98.14% <100.00%> (+0.07%)	⬆️
scrapy_zyte_api/poet.py	100.00% <100.00%> (ø)
scrapy_zyte_api/providers.py	93.00% <100.00%> (-1.15%)	⬇️
scrapy_zyte_api/_poet_item_pipelines.py	98.30% <98.30%> (ø)

... and 2 files with indirect coverage changes

[kmike]

The code looks good 👍 But I haven't checked how it works, and if it solves the issue :)

[kmike]

Moving it to scrapy-poet might allow to make the name shorter :)