2.1.2: Further Dockerfile/Workflow image building optimizations

[defunctl]

Main Changes

The last 2.1.1 build still took 30 minutes because most of it was uncached, these changes improve the caching but also significantly improve the build speeds for arm64: From 30m to 4m19s uncached!

Note

Thank you @borkweb for getting the ubuntu-24.04-arm runner enabled in our org!

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• Change - GitHub Actions workflows now use native ARM64 runners (ubuntu-24.04-arm) instead of QEMU emulation for multi-platform builds, to reduce build times.
• Change - Optimized Dockerfile layer ordering to improve cache hit rates - local config files moved to end to prevent invalidating heavy system installation layers.
• Change - Added BuildKit cache mounts for apt package installation and PHP extension compilation, to reduce subsequent build times.
• Change - Added IPE_CACHE_DIR environment variable to cache PHP extension downloads and compiled artifacts across builds.
• Change - Implemented platform-specific registry caching (separate caches for amd64/arm64) to prevent cache conflicts and maximize reuse.

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Here are some runs with these updates with maximum caching:

1. slic-wordpress-php - 1m 1s
2. slic-php - 59s

Here are the uncached arm64 builds:

1. slic-wordpress-php - 1m 55s
2. slic-php - 4m 19s

[defunctl]

@lucatume please give the arm64 images one more test when you get a chance.