ci: use gnuoctave/octave Docker container — no more apt-get install

Replace apt-get install octave on every run with pre-built Docker
container (gnuoctave/octave:8.4.0). Octave + octave-dev + xvfb are
all pre-installed. Saves ~60s per job.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: HanSur94

.github/workflows/benchmark.yml

@@ -14,6 +14,7 @@ jobs:
   build-mex:
     name: Build MEX
     runs-on: ubuntu-latest
+    container: gnuoctave/octave:8.4.0
     steps:
       - uses: actions/checkout@v4
 
@@ -26,10 +27,6 @@ jobs:
             libs/SensorThreshold/private/*.mex
           key: mex-linux-${{ hashFiles('libs/FastPlot/private/mex_src/**', 'libs/FastPlot/build_mex.m') }}
 
-      - name: Install Octave
-        if: steps.cache-mex.outputs.cache-hit != 'true'
-        run: sudo apt-get update && sudo apt-get install -y octave octave-dev
-
       - name: Compile MEX files
         if: steps.cache-mex.outputs.cache-hit != 'true'
         run: octave --eval "setup();"
@@ -47,6 +44,7 @@ jobs:
     name: Performance Benchmark
     needs: build-mex
     runs-on: ubuntu-latest
+    container: gnuoctave/octave:8.4.0
     steps:
       - uses: actions/checkout@v4
 
@@ -55,9 +53,6 @@ jobs:
         with:
           name: mex-linux-bench
 
-      - name: Install Octave and Xvfb
-        run: sudo apt-get update && sudo apt-get install -y octave xvfb
-
       - name: Run benchmark
         run: |
           xvfb-run octave --eval "

.github/workflows/examples.yml

@@ -10,6 +10,7 @@ jobs:
   build-mex:
     name: Build MEX
     runs-on: ubuntu-latest
+    container: gnuoctave/octave:8.4.0
     steps:
       - uses: actions/checkout@v4
 
@@ -22,10 +23,6 @@ jobs:
             libs/SensorThreshold/private/*.mex
           key: mex-linux-${{ hashFiles('libs/FastPlot/private/mex_src/**', 'libs/FastPlot/build_mex.m') }}
 
-      - name: Install Octave
-        if: steps.cache-mex.outputs.cache-hit != 'true'
-        run: sudo apt-get update && sudo apt-get install -y octave octave-dev
-
       - name: Compile MEX files
         if: steps.cache-mex.outputs.cache-hit != 'true'
         run: octave --eval "setup();"
@@ -43,6 +40,7 @@ jobs:
     name: Example Smoke Tests
     needs: build-mex
     runs-on: ubuntu-latest
+    container: gnuoctave/octave:8.4.0
     steps:
       - uses: actions/checkout@v4
 
@@ -51,9 +49,6 @@ jobs:
         with:
           name: mex-linux-examples
 
-      - name: Install Octave and Xvfb
-        run: sudo apt-get update && sudo apt-get install -y octave xvfb
-
       - name: Run example smoke tests
         run: |
           xvfb-run octave --eval "

.github/workflows/tests.yml

@@ -29,6 +29,7 @@ jobs:
     name: Build MEX (Linux)
     if: github.event_name != 'schedule'
     runs-on: ubuntu-latest
+    container: gnuoctave/octave:8.4.0
     steps:
       - uses: actions/checkout@v4
 
@@ -41,10 +42,6 @@ jobs:
             libs/SensorThreshold/private/*.mex
           key: mex-linux-${{ hashFiles('libs/FastPlot/private/mex_src/**', 'libs/FastPlot/build_mex.m') }}
 
-      - name: Install Octave
-        if: steps.cache-mex.outputs.cache-hit != 'true'
-        run: sudo apt-get update && sudo apt-get install -y octave octave-dev
-
       - name: Compile MEX files
         if: steps.cache-mex.outputs.cache-hit != 'true'
         run: octave --eval "setup();"
@@ -63,6 +60,7 @@ jobs:
     needs: build-mex
     if: github.event_name != 'schedule'
     runs-on: ubuntu-latest
+    container: gnuoctave/octave:8.4.0
     steps:
       - uses: actions/checkout@v4
 
@@ -71,9 +69,6 @@ jobs:
         with:
           name: mex-linux
 
-      - name: Install Octave and Xvfb
-        run: sudo apt-get update && sudo apt-get install -y octave xvfb
-
       - name: Run tests
         run: |
           xvfb-run octave --eval "