New pushes to open PRs spawn additional workflow runs without canceling existing ones, wasting CI pool capacity — a growing problem with AI-agent-driven development.

Adds `concurrency` groups to all PR-triggered workflows so a new push to a PR automatically cancels the previous run for that PR, while leaving `main` pushes and scheduled runs unaffected.

- **Affected workflows:** `buildAndTest.yml`, `buildAndTestWindows.yml`, `shortIntegrationTests.yml`, `testPycdeESI.yml`
- **Concurrency key:** `workflow-name + PR number` (for PRs) or `workflow-name + commit SHA` (for non-PR triggers, ensuring no cross-run cancellation)
- **`cancel-in-progress`** is conditioned on `pull_request` events only

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: teqdruid <1498080+teqdruid@users.noreply.github.com>