tests: lib: uuid: add heap arena for MINIMAL_LIBC compatibility

The UUID library utilities require dynamic memory allocation for certain
operations, but MINIMAL_LIBC provides no malloc heap by default. This
causes test failures when UUID functions attempt to allocate memory.

Add CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=256 to provide a minimal heap
arena sufficient for UUID operations which typically
require small heap allocations.

Signed-off-by: Mohamed Moawad <moawad@synopsys.com>

tests/lib/uuid/testcase.yaml

@@ -12,6 +12,8 @@ tests:
       - CONFIG_MBEDTLS_SHA1=y
       - CONFIG_UUID_BASE64=y
       - CONFIG_BASE64=y
+      # UUID utilities need some heap, but MINIMAL_LIBC has none by default.
+      - CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=256
   libraries.uuid.v4:
     extra_configs:
       - CONFIG_UUID_V4=y