Add a devcontainer for developing

.devcontainer/Dockerfile

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+# Use Ruby 3.3 as specified in the test matrix
+FROM ruby:3.3
+
+# Install dependencies
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends \
+    git \
+    build-essential \
+    libssl-dev \
+    libreadline-dev \
+    zlib1g-dev \
+    redis-tools \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/*
+
+# Create a non-root user
+ARG USERNAME=vscode
+ARG USER_UID=1000
+ARG USER_GID=$USER_UID
+
+RUN groupadd --gid $USER_GID $USERNAME \
+    && useradd --uid $USER_UID --gid $USER_GID -m $USERNAME \
+    && apt-get update \
+    && apt-get install -y sudo \
+    && echo $USERNAME ALL=\(root\) NOPASSWD:ALL > /etc/sudoers.d/$USERNAME \
+    && chmod 0440 /etc/sudoers.d/$USERNAME
+
+# Set the default user
+USER $USERNAME
+
+# Set working directory
+WORKDIR /workspaces/resque-scheduler
+
+# Install bundler
+RUN gem install bundler
+
+# Set environment variables for the test matrix configuration
+ENV REDIS_VERSION=latest
+ENV RESQUE=master
+ENV RUFUS_SCHEDULER=3.6
+ENV RACK_VERSION=3
+ENV COVERAGE=1

.devcontainer/README.md

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+# Dev Container for Resque Scheduler
+
+This dev container is configured to match the GitHub Actions test matrix with the following configuration:
+
+- **Ruby version**: 3.3
+- **Resque version**: master (from git)
+- **Rufus-scheduler**: 3.6
+- **Redis version**: latest
+- **Rack version**: 3
+
+## Getting Started
+
+1. Open this repository in VS Code
+2. When prompted, click "Reopen in Container" (or run the command "Dev Containers: Reopen in Container")
+3. Wait for the container to build and start
+4. Once inside the container, dependencies will be automatically installed via `bundle install`
+
+## Running Tests
+
+To run the full test suite:
+
+```bash
+bundle exec rake
+```
+
+To run a specific test file:
+
+```bash
+bundle exec ruby test/scheduler_test.rb
+```
+
+To run tests with verbose output:
+
+```bash
+VERBOSE=1 bundle exec rake
+```
+
+To run tests matching a specific pattern:
+
+```bash
+PATTERN='test/scheduler_*_test.rb' bundle exec rake
+```
+
+## Testing with Different Configurations
+
+If you want to test with different versions, you can modify the environment variables and reinstall dependencies:
+
+```bash
+# Example: Test with rufus-scheduler 3.4
+export RUFUS_SCHEDULER=3.4
+bundle install
+
+# Run tests
+bundle exec rake
+
+# Reset to original configuration
+export RUFUS_SCHEDULER=3.6
+bundle install
+```
+
+## Available Environment Variables
+
+The following environment variables are set to match the test matrix:
+
+- `REDIS_VERSION`: latest
+- `RESQUE`: master
+- `RUFUS_SCHEDULER`: 3.6
+- `RACK_VERSION`: 3
+- `COVERAGE`: 1
+
+## Services
+
+### Redis
+Redis is available at `redis://redis:6379` or via `localhost:6379` from within the container.
+
+To connect to Redis CLI:
+
+```bash
+redis-cli -h redis
+```
+
+## Troubleshooting
+
+### Bundle Install Issues
+
+If you encounter issues with bundle install, try:
+
+```bash
+bundle config set --local build.redis --with-cflags="-Wno-error=implicit-function-declaration"
+bundle install
+```
+
+### Redis Connection Issues
+
+Make sure Redis is running:
+
+```bash
+redis-cli -h redis ping
+```
+
+Should return `PONG`.
+
+### Rebuilding the Container
+
+If you need to rebuild the container from scratch:
+
+1. Run "Dev Containers: Rebuild Container" from the command palette
+2. Or delete the container and volume manually:
+   ```bash
+   docker-compose -f .devcontainer/docker-compose.yml down -v
+   ```

.devcontainer/devcontainer.json

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+{
+  "name": "Resque Scheduler Dev Container",
+  "dockerComposeFile": "docker-compose.yml",
+  "service": "app",
+  "workspaceFolder": "/workspaces/resque-scheduler",
+
+  // Features to add to the dev container
+  "features": {
+    "ghcr.io/devcontainers/features/git:1": {}
+  },
+
+  // Configure tool-specific properties
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "rebornix.ruby"
+      ],
+      "settings": {
+        "terminal.integrated.defaultProfile.linux": "bash"
+      }
+    }
+  },
+
+  // Use 'forwardPorts' to make a list of ports inside the container available locally
+  "forwardPorts": [6379],
+
+  // Use 'postCreateCommand' to run commands after the container is created
+  "postCreateCommand": "bundle install",
+
+  // Set environment variables for the test matrix
+  "containerEnv": {
+    "REDIS_VERSION": "latest",
+    "RESQUE": "master",
+    "RUFUS_SCHEDULER": "3.6",
+    "RACK_VERSION": "3",
+    "COVERAGE": "1"
+  },
+
+  // Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root
+  "remoteUser": "vscode"
+}

.devcontainer/docker-compose.yml

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+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    volumes:
+      - ../..:/workspaces:cached
+    working_dir: /workspaces/resque-scheduler
+    command: sleep infinity
+    environment:
+      REDIS_VERSION: "latest"
+      RESQUE: "master"
+      RUFUS_SCHEDULER: "3.6"
+      RACK_VERSION: "3"
+      COVERAGE: "1"
+      REDIS_URL: "redis://redis:6379"
+    depends_on:
+      - redis
+    # Runs app on the same network as the redis container, allows "forwardPorts" in devcontainer.json function
+    network_mode: service:redis
+
+  redis:
+    image: redis:latest
+    restart: unless-stopped
+    ports:
+      - "6379:6379"
+    volumes:
+      - redis-data:/data
+
+volumes:
+  redis-data: