t/unit-tests: adapt priority queue test to use clar test framework

t/unit-tests: adapt priority queue test to use clar test framework

Convert the prio-queue test script to clar framework by using clar
assertions where necessary. Test functions are created as a standalone
to test different cases.

update the type of the variable `j` from int to `size_t`, this ensures
compatibility with the type used for result_size, which is also size_t,
preventing a potential warning or error caused by comparisons between
signed and unsigned integers.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Seyi Kuforiji <kuforiji98@gmail.com>
Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>