feat(data/fintype/card): prod_univ_sum (#2284)
* feat(data/fintype/card): prod_univ_sum
* Update src/data/fintype.lean
* Update src/data/fintype/card.lean
* docstrings
* fix build
* remove unused argument
* fix build
Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: Bryan Gin-ge Chen <bryangingechen@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
