POSIX constant not available on Windows causes compile errors

[bjornblissing]

This section uses MAP_FAILED, which is a POSIX constant not available on Windows. Resulting in compilation errors.

USearch/include/usearch/index_plugins.hpp

Line 962 in 40d127f

if (!new_arena || new_arena == (byte_t*)MAP_FAILED)

Introduced by: #711