feat(data/fintype): fintype.card_subtype_lt (#1635)
feat(data/fintype): fintype.card_subtype_lt (#1635)

* feat(data/fintype): fintype.card_subtype_lt

* Update src/data/fintype.lean

Co-Authored-By: Rob Lewis <f89db59e6074667375662ee222555a187f42739f@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib