nomount: implement whiteouts, hijacking hooks and refactor code

[maxsteeel]

• kernel/:

  • Implement the NM_FLAG_WHITEOUT bitmask to explicitly hide existing physical files from the VFS.
  • Replace all in-kernel hooks in favor of hijacking of i_op / f_op / s_op structures of files.
  • Replace hashtable lookups for structure hijacking lookups for O(1) lookups in hot-paths.
  • Remove nomount_inodes_ht and nomount_inode_node. Added nm_inode_info to O(1) inode operations.
  • Fix a critical logic error by replacing bitwise masking switch statements with sequential if conditions in inode spoofing routines.
  • Replace directory child arrays to directory child IDR trees, to improve management of directory childs and also to optimize iterate_dir operations.
  • Replace UID exclusion lists/hashtables to a IDR tree for O(1) checks.
  • Add missing u8 flags member to struct nomount_child_name to allow flag inheritance.
  • Simplifying and removing dead code.

• userspace/:

  • Extend payload struct to pack NM_FLAG_WHITEOUT instructions via the new w (whiteout) command argument in the nm CLI tool.
  • Adapt the JSON and raw nm list parsers to properly identify and print whiteout entries natively from the Netlink attribute header.
  • Implement UID-based operations. Now can add, o hide files / folders for some UID's
    • Example:
    • nm add /system/etc/hosts /data/adb/modules/hosts/system/etc/hosts --uid 10100
    • nm whiteout /system/etc/lineage.prop --uid 10240
  • Replace .bss buffers for a stack-based buffers, to avoid strange bugs in some devices when .bss is ignored.
  • Solved some little bugs.

• module/:

  • Add support for traditional OverlayFS character device (mknod) and Magisk .replace syntax detection during the boot phase inside metamount.sh. In response of [Question] Delete implementation method in NoMount #16
  • Refactor xargs batching pipelines in metamount.sh and index.js to process up to the maximum ARG_MAX limit dynamically via null-byte (\0) streams.
  • Remove JSON parsing overhead from hot-unloading routines in the WebUI, opting for a direct unified file/symlink/char device file-system scan targeting nm d.
  • Implement UID exclusion list directly from kernel, to verify what's UID's are really blocked in kernel.
  • Remove the alias engine.