lib: packing: add additional KUnit tests

lib: packing: add additional KUnit tests

While reviewing the initial KUnit tests for lib/packing, Przemek pointed
out that the test values have duplicate bytes in the input sequence.

In addition, I noticed that the unit tests pack and unpack on a byte
boundary, instead of crossing bytes. Thus, we lack good coverage of the
corner cases of the API.

Add additional unit tests to cover packing and unpacking byte buffers which
do not have duplicate bytes in the unpacked value, and which pack and
unpack to an unaligned offset.

A careful reviewer may note the lack tests for QUIRK_MSB_ON_THE_RIGHT. This
is because I found issues with that quirk during test implementation. This
quirk will be fixed and the tests will be included in a future change.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://patch.msgid.link/20241002-packing-kunit-tests-and-split-pack-unpack-v2-7-8373e551eae3@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>