setup: dynamically detect default huge page size

[Kprateek283]

Replaces the hardcoded 2MB huge page size with dynamic detection by
parsing /proc/meminfo. This fixes no-mmap allocation failures on
architectures with different default huge page sizes (like ARM64
which often uses 512MB) or x86 systems configured for 1GB pages.

• Safely parses /proc/meminfo without allocating memory.
• Uses raw syscalls and manual byte-by-byte matching to maintain strict compatibility with CONFIG_NOLIBC builds (avoiding strstr).
• Drops the MAP_HUGE_2MB mmap flag to allow the kernel to correctly apply the system's default huge page size.
• Falls back safely to 2MB if /proc/meminfo is unreadable.

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git request-pull output:

The following changes since commit 2750b94a77ea9e4e156fd0caa5c14552e7d1397f:

  Merge branch 'poll-update-trigger' of https://github.com/schlad/liburing (2026-06-10 06:57:31 -0600)

are available in the Git repository at:

  https://github.com/Kprateek283/liburing.git fix-huge-page-size

for you to fetch changes up to 69c3265ab7cacbcb981f7bc6346f89ea076cf672:

  setup: dynamically detect default huge page size (2026-06-12 00:56:19 +0530)

----------------------------------------------------------------
Prateek (1):
      setup: dynamically detect default huge page size

 src/setup.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 68 insertions(+), 16 deletions(-)

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