Check pip availability before running ensurepip

[priyagupta108]

This pull request improves the robustness of the Python installation scripts across macOS, Linux, and Windows by ensuring that pip is only bootstrapped with ensurepip if it is not already present. This prevents unnecessary reinstallation and potential errors during setup.

[Copilot]

Pull request overview

This pull request improves the robustness of the Python toolcache setup templates by only running ensurepip when pip is not already importable for the target interpreter, avoiding redundant bootstrapping steps across Windows, Linux, and macOS.

Changes:

• Windows: check import pip before invoking python -m ensurepip.
• Linux/macOS: gate ./python -m ensurepip behind an import pip check (with stderr suppressed).
• Keep the existing pip install --upgrade --force-reinstall pip ... upgrade flow unchanged.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
installers/win-setup-template.ps1	Adds a pip import check before running ensurepip, then upgrades/reinstalls pip as before.
installers/nix-setup-template.sh	Runs ensurepip only when pip isn’t importable, then performs the same pip upgrade/reinstall.
installers/macos-pkg-setup-template.sh	Mirrors the nix template change: conditionally run ensurepip based on import pip, then upgrade/reinstall.

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