Fix CMake build failure on Linux due to hidapi cmake_minimum_required < 3.5

- Set CMAKE_POLICY_VERSION_MINIMUM=3.5 before FetchContent_MakeAvailable(hidapi)
  to suppress CMake 3.31+ error for sub-projects using cmake_minimum_required < 3.5
- Update hidapi from 0.14.0 to 0.15.0 (latest stable release)
- Add libudev-dev and libusb-1.0-0-dev to CI Linux dependencies for hidapi backends

Co-authored-by: CommanderPho <962210+CommanderPho@users.noreply.github.com>

Author: Copilot

.github/workflows/build.yml

@@ -61,7 +61,8 @@ jobs:
         if: runner.os == 'Linux'
         run: |
           sudo apt-get update
-          sudo apt-get install -y libgl1-mesa-dev libxkbcommon-dev libxcb-cursor0
+          sudo apt-get install -y libgl1-mesa-dev libxkbcommon-dev libxcb-cursor0 \
+            libudev-dev libusb-1.0-0-dev
 
       - name: Install Qt
         uses: jurplel/install-qt-action@v4

CMakeLists.txt

@@ -80,11 +80,16 @@ if(EMOTIVLSL_BUILD_EMOTIV)
     FetchContent_Declare(
         hidapi
         GIT_REPOSITORY https://github.com/libusb/hidapi.git
-        GIT_TAG        hidapi-0.14.0
+        GIT_TAG        hidapi-0.15.0
         GIT_SHALLOW    ON
         EXCLUDE_FROM_ALL
     )
+    # hidapi uses cmake_minimum_required(VERSION 3.1.3), which CMake 3.31+
+    # no longer supports (compatibility with < 3.5 was removed). Setting
+    # CMAKE_POLICY_VERSION_MINIMUM suppresses the error for sub-projects.
+    set(CMAKE_POLICY_VERSION_MINIMUM "3.5")
     FetchContent_MakeAvailable(hidapi)
+    unset(CMAKE_POLICY_VERSION_MINIMUM)
 
     # tiny-AES-c (ECB decryption for Emotiv data stream)
     # We only need the source files, not a built library, so we use SOURCE_DIR-only population.