need a simple version of memory allocation lib for test_size

[jyao1]

Current version is https://github.com/DMTF/libspdm/tree/main/unit_test/test_size/malloclib_null. But it does not have any functionality.

We need a simple version of memory allocation lib for test_size, to make data more accurately.

Reference: https://github.com/tianocore/edk2/blob/master/CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c