📦 Add pip-supported extra for upper bound

[webknjaz]

It is supposed to correspond to the range of what's tested in our CI.

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• Included tests for the changes.
• A change note is created in changelog.d/ (see changelog.d/README.md for instructions) or the PR text says "no changelog needed".

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[webknjaz]

We'll need some sort of linting for keeping these in sync w/ CI and perhaps docs.

[Copilot]

Pull Request Overview

This PR introduces version constraints for pip to ensure compatibility testing. It adds a new optional dependency group called supported-pip that limits pip to versions below 25.3, and integrates this constraint into the tox testing environments for pipsupported and piplowest configurations.

• Added a new supported-pip optional dependency group in pyproject.toml with pip version constraint < 25.3
• Updated tox configuration to use the supported-pip extras for pipsupported and piplowest test environments

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pyproject.toml	Adds supported-pip optional dependency group with pip version constraint
tox.ini	Integrates supported-pip extras into pipsupported and piplowest test environments

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[sirosen]

I am trying to decide what we should name this extra -- not taking it as a given that the proposed name, supported-pip, is best.

I think supported-pip may be confusing if we start pinning anything other than pip in the future. And I think we should at least start with pip-only, which makes the possibility of such confusion stronger in the future. So I think we should remove pip from the name of the extra.

That would leave us with pip-tools[supported], which I think is good. I can't come up with anything better, at least!

[webknjaz]

I think supported-pip may be confusing if we start pinning anything other than pip in the future. And I think we should at least start with pip-only, which makes the possibility of such confusion stronger in the future. So I think we should remove pip from the name of the extra.

That would leave us with pip-tools[supported], which I think is good. I can't come up with anything better, at least!

That's a good point. Alternatively, we could have multiple composable extras and the users could use pip-tools [supported-click, supported-pip].