Add Docker layer caching for development builds

[nevoodoo]

Summary

This PR implements Docker layer caching to significantly speed up CI builds for development branches while keeping production builds clean and reproducible.

Changes

1. GitHub Workflow - Switched to docker/build-push-action

• Replaced manual docker pull/build/push commands with docker/build-push-action
• Uses GitHub Actions cache (type=gha) for fast layer caching
• Development builds benefit from caching; production builds use no-cache: true
• Security: Fixed code injection vulnerability by using environment variables instead of direct github.ref_name interpolation

2. Dockerfile - Optimized for layer caching

• Follows uv's official Docker pattern with bind mounts
• Separates dependency installation from source code copying
• Uses --locked flag (uv's recommended option for Docker)
• Uses --no-dev to exclude development dependencies from production image
• Combines GitHub Actions cache (layer reuse) with UV cache mount (package download caching)

[cpg-software-ci-bot]

📊 SonarQube Summary

Metric	This PR	Main Branch
✅ Coverage	76.3%	76.3%
💨 Code Smells	47	13
🐞 Bugs	0	0
🔐 Vulnerabilities	0	0
🚨 Security Hotspots	1	0
📝 New Issues	0	0
🌟 Quality Gate	✅ OK	✅ OK

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[github-actions]

🐳 Docker Image Built

A new Docker image has been built for this PR:

Image: australia-southeast1-docker.pkg.dev/cpg-common/images-dev/cpg_flow:5a9a021727776b58f3781c6128a0d2efb95a54a5

Pull command:

docker pull australia-southeast1-docker.pkg.dev/cpg-common/images-dev/cpg_flow:5a9a021727776b58f3781c6128a0d2efb95a54a5

🔗 View in Google Cloud Console

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