Expose mimalloc allocations for profiler interposition

[pablogsal]

Memory profilers like memray couldn't track Arrow's mimalloc allocations because mimalloc is statically linked into libarrow.so and internal calls bypass PLT. This adds weak exported wrapper functions (arrow_mimalloc_allocate, arrow_mimalloc_reallocate, arrow_mimalloc_free) that route through PLT even for intra-DSO calls, enabling LD_PRELOAD-based interposition.

Includes a test that verifies the interposition mechanism works by preloading a tracking library and checking allocation counts.

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[github-actions]

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[pablogsal]

Ah i was not aware of #41128 @pitrou do yo think you can resurrect that PR, with that we can add memray support