[Perf] Fix memory gauge crash using task_info (#16121)

[JesusRojass]

FPRMemoryGaugeCollector samples app memory on a timer. On iOS 17 and later
devices running the XZone Malloc (XZM) allocator, the malloc zone statistics
call crashes inside xzm_statistics_self while taking a non-reentrant allocator
lock, killing the process with EXC_BAD_ACCESS / EXC_BREAKPOINT.

12.10.0 (#15595) replaced mstats() with malloc_zone_statistics() to address
#15501. However mstats() is a thin wrapper around
malloc_zone_statistics(NULL, &s), so the crashing call path was unchanged and
reports kept coming in (#16121).

This change collects memory with task_info(mach_task_self(), TASK_VM_INFO, ...)
and reads phys_footprint instead. task_info is a kernel RPC that does not
touch libmalloc and takes no userspace allocator lock, so it cannot reach
xzm_statistics_self. This removes the crash. It also matches the Mach API
approach already used by FPRCPUGaugeCollector.

Behavior note: phys_footprint is the per-process physical memory footprint
(the value Jetsam accounting and the Xcode memory gauge use). It is not a
heap-only statistic; it includes heap memory along with other dirty and
compressed pages. heapUsed now carries phys_footprint, and heapAvailable
is reported as 0 because phys_footprint reports only used memory. The backend
field free_app_heap_memory_kb will therefore be 0.

Fixes #16121

Testing

• Existing FPRMemoryGaugeCollector unit tests pass.
• Validated on a physical device running iOS 17+.

API Changes

• No API Changes

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[JesusRojass]

Work in progress!!!

[JesusRojass]

/gemini review

[gemini-code-assist]

Code Review

This pull request replaces the use of malloc_zone_statistics with task_info(TASK_VM_INFO) in FPRMemoryGaugeCollector to prevent crashes on devices using the XZM allocator. It also updates the corresponding documentation, tests, and changelog. The review feedback suggests initializing the vmInfo struct to zero to avoid reading uninitialized stack memory and verifying that the returned count is at least TASK_VM_INFO_REV1_COUNT before accessing phys_footprint to ensure it was populated by the kernel.

[JesusRojass]

/gemini review

[gemini-code-assist]

Code Review

This pull request replaces the use of malloc_zone_statistics with task_info(TASK_VM_INFO) in FPRMemoryGaugeCollector to prevent crashes on devices using the XZM allocator. It also updates the associated documentation and adds unit tests to verify the new memory collection behavior. The review feedback suggests simplifying the memory collection logic by removing the unused freeBytes variable and improving the debug logging to distinguish between a failed task_info call and an insufficient returned data count.

[JesusRojass]

Ready for review @tejasd