feat(mem): add KernelStack field for ExVirtualMemory on linux

[shirou]

This is a PR under #1884. But this PR moves KernelStack field to ExVirtualMemory because that is Linux only .

[Copilot]

Pull request overview

This PR adds the KernelStack field to both the VirtualMemoryStat struct and the Linux-specific ExVirtualMemory struct. This field was previously missing but is available in Linux's /proc/meminfo. The change ensures that kernel stack memory usage is captured and exposed through both the general and extended memory statistics APIs on Linux.

Key Changes:

• Added KernelStack field to VirtualMemoryStat struct with camelCase JSON tag
• Added KernelStack field to Linux-specific ExVirtualMemory struct
• Updated Linux parsing logic to populate both KernelStack fields from /proc/meminfo

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
mem/mem.go	Added KernelStack field to VirtualMemoryStat struct between Sunreclaim and PageTables
mem/ex_linux.go	Added KernelStack field to Linux-specific ExVirtualMemory struct
mem/mem_linux.go	Added parsing logic for KernelStack from /proc/meminfo, populating both main and extended memory stats
mem/mem_test.go	Updated expected JSON string in test to include kernelStack field
mem/mem_linux_test.go	Added KernelStack values to test cases where the field is present in corresponding test data files

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