lib: test_objagg: split test_hints_case() into two functions

With sanitizers enabled, this function uses a lot of stack, causing
a harmless warning:

lib/test_objagg.c: In function 'test_hints_case.constprop':
lib/test_objagg.c:994:1: error: the frame size of 1440 bytes is larger than 1408 bytes [-Werror=frame-larger-than=]

Most of this is from the two 'struct world' structures. Since most of
the work in this function is duplicated for the two, split it up into
separate functions that each use one of them.

The combined stack usage is still the same here, but there is no warning
any more, and the code is still safe because of the known call chain.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20250620111907.3395296-1-arnd@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>