# In this task, we will add persistence to the ‹Shelter› class from
# the previous installment (‹t1_shelter›). You should provide 2 new
# functions, ‹load› and ‹store›. The basic requirement is that doing a
# ‹store› → ‹load› → ‹store› sequence will produce two identical
# copies of the same data.
#
#  • Both ‹load› and ‹store› expect a ‹db› keyword argument, which
#    takes an open ‹sqlite3› connection.
#  • The ‹load› function accepts a single positional argument, an id
#    of the ‹Shelter› snapshot to load and returns a ‹Shelter›
#    instance.
#  • The ‹store› function takes a ‹Shelter› instance as its only
#    positional argument, and returns an id (which can be then
#    passed to ‹load›).
#
# Please note that storing multiple ‹Shelter› instances in a single
# database must be possible. Moreover, each animal and human should
# appear in the entire database only once, even if they appear in
# multiple ‹Shelter› snapshots stored in that database. We consider
# two people or two animals the same if all their attributes match,
# with two exceptions:
#
#  • the ‹max_capacity› of a foster parent: the same foster parent
#    may appear in multiple ‹Shelter› instances with a different
#    capacity,
#  • the ‹date_of_entry› of an animal, which works the same way
#    (the same animal still cannot re-enter the same shelter though).
#
# Beware! This is a departure from the semantics required in
# ‹t1_shelter›, where it was possible to have multiple animals with
# identical attribute sets. For this assignment, you will need to
# modify ‹add_animal› to return an existing object if all attributes
# match (again with the exception of ‹date_of_entry›: if all other
# attributes match but not ‹date_of_entry›, raise a ‹RuntimeError›).
#
# Same with foster parents and ‹max_capacity›. A foster parent and an
# adopter with the same name and address are, however, distinct
# entities and should be allowed. In this case, the name and address
# will repeat in the database (once as a foster parent and once as an
# adopter).
#
# Finally, if ‹store› is called on a ‹Shelter› with the keyword
# argument ‹deduplicate› set to ‹True›, and a snapshot with the
# exact same information (i.e. the list of animals, adopters, foster
# parents, fostering records and vet exams) is already present, do
# not add anything to the database and return the id of the existing
# snapshot. It is okay for this check to be, in the worst case,
# linear in the number of snapshots already stored.
#
# The database schema is up to you, subject to the constraints above.
# If ‹store› is called on an empty database, it should create the
# necessary tables.