test-cutils: Use g_assert_cmpuint where appropriate

When debugging test failures, seeing unsigned values as large positive
values rather than negative values matters (assuming glib 2.78+; given
that I just fixed a bug in glib 2.76 [1] where g_assert_cmpuint
displays signed instead of unsigned values).  No impact when the test
is passing, but using a consistent style will matter more in upcoming
test additions.  Also, some tests are better with cmphex.

While at it, fix some spacing and minor typing issues spotted nearby.

[1] https://gitlab.gnome.org/GNOME/glib/-/issues/2997

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20230522190441.64278-3-eblake@redhat.com>