The PHP feature has a very bad performance (in GitHub Codespaces)

I can use this e.g. as the image: `mcr.microsoft.com/devcontainers/php`

In GitHub Codespaces that results in _that_:

It is slow, very slow, because – I guess – it _literally_ compiles PHP – given [it depends on the official PHP docker container](https://github.com/devcontainers/images/blob/992d14db469202201020633827c2eb8857ba3ea7/src/php/.devcontainer/Dockerfile#L3) and they famously compile Docker from scratch there.

I just wonder why nothing is cached? Afterall, it should not build for minutes and these basic images should be cached.
For "quick development", which GitHub Codespaces is aimed at, that is a no-go.

This is my full `.devcontainer` file:
```json
{
"name": "PHP",
"image": "mcr.microsoft.com/devcontainers/php",
"customizations": {
"vscode": {
"extensions": [
"github.codespaces",
"DEVSENSE.phptools-vscode",
"EditorConfig.EditorConfig",
"dbaeumer.vscode-eslint",
"raymondcamden.CSSLint",
"DEVSENSE.composer-php-vscode"
]
},
"codespaces": {
"repositories": {
"PrivateBin/*": {
"permissions": {
"pull_requests": "write"
}
}
}
}
},
"forwardPorts": [
8080
],
"features": {
"ghcr.io/devcontainers/features/php:1": {
"installComposer": true,
"version": "latest"
}
},
"postCreateCommand": "sudo chmod a+x \"$(pwd)\" && sudo rm -rf /var/www/html && sudo ln -s \"$(pwd)\" /var/www/html",
"postStartCommand": "apache2ctl start"
}
```

Reproduce el problema utilizando la configuración .devcontainer proporcionada y la imagen mcr.microsoft.com/devcontainers/php. Compara la instalación de la feature de PHP con el Dockerfile de devcontainers/images enlazado, centrándote en por qué el trabajo relacionado con PHP se vuelve a compilar en lugar de utilizar la caché. Se considera completado cuando se haya identificado la causa y la configuración de Codespaces ya no tarde varios minutos en estar utilizable.

Escrito por el modelo de indexación a partir del texto del issue.