chore: drop the liburing prerequisite, which was never used

IORingGroup issues io_uring syscalls directly rather than linking
liburing, so the package was never needed. Checked against the shipped
IORingGroup 1.0.9 assembly: its P/Invoke targets are libc,
libSystem.dylib, kernel32.dll, kernelbase.dll and ws2_32.dll. It
contains no reference to liburing and no call to io_uring_queue_init,
liburing's entry point -- only the raw io_uring_setup syscall.

Removes it from the README, from CI, and from the three places
NativeLibraryChecker asked for it (the cross-compile target text, the
apt and dnf package lists, and the ldconfig fallback map).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/build-test.yml

@@ -125,10 +125,10 @@ jobs:
           dnf install -y epel-release
         if: ${{ matrix.epel }}
       - name: Install Prerequisites using dnf
-        run: dnf makecache --refresh && dnf install -y findutils libicu libdeflate-devel zstd libargon2-devel liburing-devel
+        run: dnf makecache --refresh && dnf install -y findutils libicu libdeflate-devel zstd libargon2-devel
         if: ${{ matrix.packageManager == 'dnf' }}
       - name: Install Prerequisites using apt
-        run: apt-get update -y && apt-get install -y curl libicu-dev libdeflate-dev zstd libargon2-dev tzdata liburing-dev
+        run: apt-get update -y && apt-get install -y curl libicu-dev libdeflate-dev zstd libargon2-dev tzdata
         if: ${{ matrix.packageManager == 'apt' }}
       - uses: actions/checkout@v7
         with: