CI: fan out Azure pipelines on Python version (parallel matrix) - speedup x5

[GuillemSeCa]

Problem

In etc/ci/azure-posix.yml and etc/ci/azure-win.yml, python_versions are iterated as a sequential template loop inside a single job's steps:, instead of being part of strategy.matrix. So each (os, test_suite) runs all Python versions back-to-back on the same agent VM.

Two visible consequences:

1. Long wall-clock time — e.g. ubuntu24_cpython all runs 3.10 → 3.11 → 3.12 → 3.13 → 3.14 in series (~10 min each = ~50 min total).
2. Cascading skips — if the first Python version's tests fail (recently happened on the *_latest_from_pip matrix because of a click 8.2 error-message change), all later Python versions are marked skipped instead of also running, hiding whether they're affected too.

Example from a recent UV PR run:

Python	Result
3.10	failed
3.11	skipped
3.12	skipped
3.13	skipped
3.14	skipped

Change

Move python_version into strategy.matrix (alongside test_suite) in both templates so each (python_version, test_suite) combination runs as its own parallel job on its own agent VM.

Matrix keys are of the form py3_10_all, py3_11_misc_and_scancode, etc. (Azure matrix keys must be alphanumeric+underscore, so dots in version strings are replaced).

No changes to caller pipelines in azure-pipelines.yml — the python_versions and test_suites parameters keep the same shape.

Tradeoffs

Aspect	Before	After
Wall-clock for ubuntu24_cpython all (5 pyvers)	~50 min	~10 min
Visibility of multi-version failures	Stops at first fail	All versions reported
Concurrent agent slots needed	1 per (os, suite)	N per (os, suite), where N = #pyvers
Setup overhead	Configure once per agent	Configure per (pyver, suite) pair

⚠️ Capacity caveat: This expands the total number of concurrent jobs. The free Azure DevOps OSS tier provides ~10 concurrent agents. If the project's available concurrency can't absorb the fan-out, jobs will queue instead of running in parallel and overall wall-clock won't improve. Maintainers should confirm available capacity before merging.

Marked as draft for that reason — merge at your discretion.

Guillem Serra Cazorla gserracazorla@gmail.com