Adds limit for nested dict stats computation

[mrwbarg]

Closes #416 Adds a setting to limit how deep the coverage is computed for nested dicts.

[curita]

The CI issues have been fixed 🙏 Could you rebase/merge the latest changes from master? @mrwbarg

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (377c4ab) 79.39% compared to head (1281600) 79.42%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #421      +/-   ##
==========================================
+ Coverage   79.39%   79.42%   +0.03%     
==========================================
  Files          76       76              
  Lines        3222     3228       +6     
  Branches      534      536       +2     
==========================================
+ Hits         2558     2564       +6     
  Misses        593      593              
  Partials       71       71              

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[curita]

@Gallaecio @rennerocha could you check on this PR? It's ready to be reviewed.

[VMRuiz]

Can we close this in favor of https://github.com/scrapinghub/spidermon/pull/433 ?