adopt ni/python-actions for PR builds

[mshafer-NI]

Justification

We are aligning on action templates in ni/python-actions

The publishing code was already moved over to unblock it, now, let's get the PR pipelines switched over as well.

Major changes

• Drop support for Python 3.8
• Start using poetry 2 for PR builds
• Add 3.14 and 3.14-free-threaded (3.14t) to the test matrix

Testing

PR should execute the modified actions

[github-actions]

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[Copilot]

Pull Request Overview

This PR migrates the CI/CD pipeline to use standardized actions from ni/python-actions and modernizes Python version support by dropping Python 3.8 and adding Python 3.14 (including the free-threaded variant).

Key changes:

• Updated minimum Python version from 3.8 to 3.9
• Adopted ni/python-actions templates for setup-python, setup-poetry, and analyze-project steps
• Added Python 3.14 and 3.14t (free-threaded) to the test matrix

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
pyproject.toml	Updated minimum Python version to 3.9 and simplified flake8-tidy-imports dependency constraint
poetry.toml	Added configuration to create virtualenvs in-project for better CI caching
poetry.lock	Updated lock file to reflect Python 3.9 minimum and removed flake8-tidy-imports 4.10.0
.github/workflows/PR.yml	Migrated to ni/python-actions, expanded checks to run on all platforms, and added Python 3.14/3.14t support

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