fix (perf/UX): get physical cores for Windows

[jon-chuang]

Complete #934 with the windows impl of physical cores

The impl is approximately:

DWORD buffer_size = 0;
DWORD result = GetLogicalProcessorInformation(NULL, &buffer_size);
// assert result == FALSE && GetLastError() == ERROR_INSUFFICIENT_BUFFER
PSYSTEM_LOGICAL_PROCESSOR_INFORMATION buffer = (PSYSTEM_LOGICAL_PROCESSOR_INFORMATION)malloc(buffer_size);
result = GetLogicalProcessorInformation(buffer, &buffer_size);
if (result != FALSE) {
    int num_physical_cores = 0;
    DWORD_PTR byte_offset = 0;
    while (byte_offset < buffer_size) {
        if (buffer->Relationship == RelationProcessorCore) {
            num_physical_cores++;
        }
        byte_offset += sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION);
        buffer++;
    }
    std::cout << "Number of physical cores: " << num_physical_cores << std::endl;
} else {
    std::cerr << "Error getting logical processor information: " << GetLastError() << std::endl;
}
free(buffer);

The location of the change is here: https://github.com/ggerganov/llama.cpp/blob/4a98a0f21ad63d97a643ba6fb21f613cb596cb23/examples/common.cpp#L57

[github-actions]

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