Add number of products to product finder

[akaszynski]

Thanks to the tip by @fret423, we can add the number of products returned by the product_finder query.

[codecov[bot]]

Codecov Report

Merging #151 (1329049) into main (0af5971) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #151   +/-   ##
=======================================
  Coverage   90.45%   90.45%           
=======================================
  Files           4        4           
  Lines         587      587           
=======================================
  Hits          531      531           
  Misses         56       56           

Files	Coverage Δ
src/keepa/interface.py	90.17% <100.00%> (ø)