When light (or comprehensive) poisoning is enabled, the size requested by the user for allocation
is extended by a few bytes to store the canary header and footer. heap_caps_get_allocated_size() should
return the original size asked by the user (without the additional canary bytes).
test_malloc.c extended with a new test assuring that heap_caps_get_allocated_size() returns the proper size
regardless of the degree of poisoning.
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