t/unit-tests: convert oid-array test to use clar test framework

t/unit-tests: convert oid-array test to use clar test framework

Adapt oid-array test script to clar framework by using clar assertions
where necessary. Remove descriptions from macros to reduce
redundancy, and move test input arrays to global scope for reuse across
multiple test functions. Introduce `test_oid_array__initialize()` to
explicitly initialize the hash algorithm.

These changes streamline the test suite, making individual tests
self-contained and reducing redundant code.

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