Support linux aarch64 for Dart and Flutter (#2342)

Adds support for building and packaging Linux AArch64 (arm64) artifacts alongside x64 for Dart/Flutter plugins.

- Detects host architecture in CMake and adjusts library paths
- Extends test workflows to run on an ARM runner and handle linux-aarch64 paths
- Splits release pipeline into separate x64 and aarch64 build/package jobs

.github/workflows/test-dart.yaml

@@ -32,7 +32,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest] #, windows-latest]
+        os: [ubuntu-latest, macos-latest, ubuntu-24.04-arm] #, windows-latest]
 
     steps:
       - uses: actions/checkout@v4
@@ -50,11 +50,12 @@ jobs:
         with:
           key: ${{ matrix.os }}-dart
 
-      - name: Setup Flutter SDK
-        uses: flutter-actions/setup-flutter@v3
+      # see https://github.com/subosito/flutter-action/issues/345
+      - name: Set up Flutter
+        uses: subosito/flutter-action@v2
         with:
-          channel: stable
-          version: latest
+          channel: master
+          flutter-version: 3.24.0
 
       - name: Display flutter info
         shell: bash
@@ -91,22 +92,34 @@ jobs:
         shell: bash
         run: |
           if [[ ${{ matrix.os }} == ubuntu-latest ]]; then
-            os=linux
+            os=linux-x64
+          elif [[ ${{ matrix.os }} == ubuntu-24.04-arm ]]; then
+            os=linux-aarch64
           elif [[ ${{ matrix.os }} == macos-latest ]]; then
             os=macos
           elif [[ ${{ matrix.os }} == windows-latest ]]; then
             os=windows
           fi
 
+          echo "os: $os"
+
           if [[ $os == windows ]]; then
             cp -fv build/install/lib/*.dll ./flutter/sherpa_onnx_$os/$os
+          elif [[ $os == linux-x64 ]]; then
+            cp -fv build/install/lib/lib* ./flutter/sherpa_onnx_linux/linux/x64
+          elif [[ $os == linux-aarch64 ]]; then
+            cp -fv build/install/lib/lib* ./flutter/sherpa_onnx_linux/linux/aarch64
           else
             cp -fv build/install/lib/lib* ./flutter/sherpa_onnx_$os/$os
           fi
 
           echo "--------------------"
 
-          ls -lh ./flutter/sherpa_onnx_$os/$os
+          if [[ $os == linux-x64 || $os == linux-aarch64 ]]; then
+            ls -lh ./flutter/sherpa_onnx_linux/linux/*
+          else
+            ls -lh ./flutter/sherpa_onnx_$os/$os
+          fi
 
       - name: Run tests
         shell: bash