lib/tests: convert test_min_heap module to KUnit

lib/tests: convert test_min_heap module to KUnit

Move lib/test_min_heap.c to lib/tests/min_heap_kunit.c and convert it to
use KUnit.

This change switches the ad-hoc test code to standard KUnit test cases.
The test data remains the same, but the verification logic is updated to
use KUNIT_EXPECT_* macros.

Also remove CONFIG_TEST_MIN_HEAP from arch/*/configs/* because it is no
longer used.  The new CONFIG_MIN_HEAP_KUNIT_TEST will be automatically
enabled by CONFIG_KUNIT_ALL_TESTS.

The reasons for converting to KUnit are:

1. Standardization:
    Switching from ad-hoc printk-based reporting to the standard
    KTAP format makes it easier for CI systems to parse and report test
    results

2. Better Diagnostics:
    Using KUNIT_EXPECT_* macros automatically provides detailed
    diagnostics on failure.

3. Tooling Integration:
    It allows the test to be managed and executed using standard
    KUnit tools.

Link: https://lkml.kernel.org/r/20251221133516.321846-1-sakamo.ryota@gmail.com
Signed-off-by: Ryota Sakamoto <sakamo.ryota@gmail.com>
Acked-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: David Gow <davidgow@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>