Dockerfile: allow to override Docker client proxy settings

[Wenzel]

If proxy settings are configured in ~/.docker/config.json, redeclaring the proxy env vars as ARG allow us to override them in all build stages.

[Copilot]

Pull Request Overview

This PR enables overriding Docker client proxy settings configured in ~/.docker/config.json by declaring proxy environment variables as ARG directives in the Dockerfile.

Key Changes:

• Added proxy ARG declarations (http_proxy, https_proxy, no_proxy) at the top of the Dockerfile
• Redeclared these ARGs in each build stage to ensure proxy settings propagate throughout the multi-stage build

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