Use wat instead of wabt to avoid CI cmake error (and use supported dep)

[jsdw]

Eg https://github.com/paritytech/subxt/actions/runs/14222244509/job/39853903005?pr=1979

error: failed to run custom build command for `wabt-sys v0.8.0`

Caused by:
  process didn't exit successfully: `/home/runner/work/subxt/subxt/target/release/build/wabt-sys-ad110709af9755cf/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-env-changed=WABT_CXXSTDLIB
  cargo:rerun-if-env-changed=CXXSTDLIB
  CMAKE_TOOLCHAIN_FILE_x86_64-unknown-linux-gnu = None
  CMAKE_TOOLCHAIN_FILE_x86_64_unknown_linux_gnu = None
  HOST_CMAKE_TOOLCHAIN_FILE = None
  CMAKE_TOOLCHAIN_FILE = None
  CMAKE_GENERATOR_x86_64-unknown-linux-gnu = None
  CMAKE_GENERATOR_x86_64_unknown_linux_gnu = None
  HOST_CMAKE_GENERATOR = None
  CMAKE_GENERATOR = None
  CMAKE_PREFIX_PATH_x86_64-unknown-linux-gnu = None
  CMAKE_PREFIX_PATH_x86_64_unknown_linux_gnu = None
  HOST_CMAKE_PREFIX_PATH = None
  CMAKE_PREFIX_PATH = None
  CMAKE_x86_64-unknown-linux-gnu = None
  CMAKE_x86_64_unknown_linux_gnu = None
  HOST_CMAKE = None
  CMAKE = None
  running: cd "/home/runner/work/subxt/subxt/target/release/build/wabt-sys-efeaddc971e9e17f/out/build" && CMAKE_PREFIX_PATH="" LC_ALL="C" "cmake" "/home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/wabt-sys-0.8.0/wabt" "-DBUILD_TESTS=OFF" "-DBUILD_TOOLS=OFF" "-DCMAKE_INSTALL_PREFIX=/home/runner/work/subxt/subxt/target/release/build/wabt-sys-efeaddc971e9e17f/out" "-DCMAKE_C_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE_C_COMPILER=/usr/bin/cc" "-DCMAKE_CXX_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE_CXX_COMPILER=/usr/bin/c++" "-DCMAKE_ASM_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE_ASM_COMPILER=/usr/bin/cc" "-DCMAKE_BUILD_TYPE=Release"
  -- Configuring incomplete, errors occurred!

  --- stderr
  CMake Error at CMakeLists.txt:17 (cmake_minimum_required):
    Compatibility with CMake < 3.5 has been removed from CMake.

    Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
    to tell CMake that the project requires at least <min> but has been updated
    to work with policies introduced by <max> or earlier.

    Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.



  thread 'main' panicked at /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cmake-0.1.50/src/lib.rs:1098:5:

  command did not execute successfully, got: exit status: 1

  build script failed, must exit now
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

wabt hasn't been updated in 4 years and binds to some C crate. wat, afaict, it a pure rust crate. We only use the crate in a couple of WASM smart contracts, anyway.