Use Namespace runners for applicable Windows builds

[zaniebot]

Windows distribution builds currently use Depot, while the pythonbuild crate runs on GitHub-hosted runners. Move the VS 2022 x86 and x86-64 distribution builds to the existing namespace-profile-windows-2022-x86-64-16x32 profile. Use the same runner lookup for crate builds, selecting Namespace for x86-64 and the native windows-11-arm runner for ARM64. ARM64 distributions and the x86-64 Python 3.15 builds that require VS 2026 continue to use their existing GitHub runners.

Five independent successful executions per workload and side compare 5b36002d with pinned main at 3fb62eb4. The x86-64 Build step is 10.6% faster; the i686 interval includes no change. Durations below are geometric means in m:ss; changes are relative to main, with unpaired Welch t 90% confidence intervals on log runtime.

Python 3.14 PGO workload	Metric	Main	Namespace	Runtime change (90% CI)
i686	Build	14:28	14:22	-0.6% (-12.9% to +13.4%)
i686	Whole job	16:59	15:57	-6.1% (-16.4% to +5.4%)
x86_64	Build	14:50	13:16	-10.6% (-15.2% to -5.7%)
x86_64	Whole job	17:23	14:23	-17.3% (-21.8% to -12.5%)

The comparison is depot-windows-2022-8 versus namespace-profile-windows-2022-x86-64-16x32, so it measures the provider, runner size, and image together. Both select Windows 2022/VS 2022, but neither provider records a precise OS-image release in the accepted job setup logs. The source differs only in runner selection. Whole-job timing excludes queue and dependency wait, and includes Generate attestations only on main. Cached pythonbuild crate builds are outside these CPython measurements.

Runtime samples

Each link gives the attempt number and Build/whole-job duration in m:ss. Untouched jobs copied into later partial reruns are counted once.

Workload	Revision	Samples
i686	Main	a1: 14:27/16:54, a2: 14:32/16:59, a9: 14:29/17:07, a14: 14:21/16:49, a19: 14:29/17:06
i686	Namespace	a1: 13:09/14:24, a2: 18:03/18:55, a4: 13:11/14:09, a6: 14:55/17:06, a8: 13:07/15:39
x86_64	Main	a1: 14:41/17:04, a3: 14:46/17:22, a10: 14:57/17:31, a15: 14:57/17:37, a20: 14:49/17:22
x86_64	Namespace	a1: 13:44/14:39, a3: 12:17/13:05, a5: 14:11/15:20, a7: 13:17/14:39, a9: 12:54/14:18

The failed i686 Cygwin download was retried and excluded from the runtime samples.