Related to #46133
Move jemalloc_stats.go and its test file from pkg/util/hardware to
internal/util/segcore. This is a more appropriate location because:
- jemalloc_stats depends on milvus_core C++ library via cgo
- The pkg directory should remain independent of internal C++
dependencies
- segcore is the natural home for core memory allocator utilities
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## Summary by CodeRabbit
* **Refactor**
* Improved internal code organization by reorganizing memory statistics
collection infrastructure for better maintainability and modularity. No
impact on end-user functionality or behavior.
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settings.</sub>
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Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>
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