Optimize PR CI with custom Docker image

.ci/container/Dockerfile

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+FROM ubuntu:24.04
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+# Install common tools and dependencies
+RUN apt-get update && apt-get install -y \
+    curl \
+    wget \
+    unzip \
+    zip \
+    git \
+    python3 \
+    xvfb \
+    ant \
+    maven \
+    libncurses6 \
+    sudo \
+    openjdk-17-jdk \
+    openjdk-21-jdk \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Java 8 (Zulu FX)
+RUN mkdir -p /usr/lib/jvm
+# Using a specific version of Zulu 8 with FX
+RUN wget -q https://cdn.azul.com/zulu/bin/zulu8.82.0.21-ca-fx-jdk8.0.432-linux_x64.tar.gz -O /tmp/java8.tar.gz \
+    && tar -xzf /tmp/java8.tar.gz -C /usr/lib/jvm \
+    && mv /usr/lib/jvm/zulu8.82.0.21-ca-fx-jdk8.0.432-linux_x64 /usr/lib/jvm/java-8-zulu-fx \
+    && rm /tmp/java8.tar.gz
+
+# Download cn1-binaries
+# We download it to /opt/cn1-binaries so it can be reused
+RUN wget -q https://github.com/codenameone/cn1-binaries/archive/refs/heads/master.zip -O /tmp/cn1-binaries.zip \
+    && unzip -q /tmp/cn1-binaries.zip -d /opt \
+    && mv /opt/cn1-binaries-master /opt/cn1-binaries \
+    && rm /tmp/cn1-binaries.zip
+
+# Set convenient env vars
+ENV JAVA_HOME_8=/usr/lib/jvm/java-8-zulu-fx
+ENV JAVA_HOME_17=/usr/lib/jvm/java-17-openjdk-amd64
+ENV JAVA_HOME_21=/usr/lib/jvm/java-21-openjdk-amd64
+
+ENV CN1_BINARIES=/opt/cn1-binaries

.github/workflows/build-container.yml

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+name: Build Container
+
+on:
+  push:
+    paths:
+      - '.ci/container/Dockerfile'
+      - '.github/workflows/build-container.yml'
+  workflow_dispatch:
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Log in to the Container registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Lowercase Repository Name
+        id: string
+        uses: ASzc/change-string-case-action@v5
+        with:
+          string: ${{ github.repository }}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v4
+        with:
+          context: .ci/container
+          push: true
+          tags: ghcr.io/${{ steps.string.outputs.lowercase }}/pr-ci-container:latest