[GSoC][PATCH] t: port reftable/basics_test.c to the unit testing

In the recent codebase update (commit 8bf6fbd, 2023-12-09), a new unit testing framework written entirely in C was introduced to the Git project aimed at simplifying testing and reducing test run times.

Currently, tests for the raftable refs-backend are performed by a custom testing framework defined by reftable/test_framework.{c, h}. Port reftable/basics_test.c to the unit testing framework and improve upon the ported test.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>