who: implement for Windows

[wtcpython]

who was previously unavailable on Windows.

This adds a backend backed by WTS session information and enables it in the Windows feature set. Option parsing and output formatting remain shared with the Unix implementation.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[codspeed-hq]

Merging this PR will improve performance by 18.85%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 366 untouched benchmarks
⏩ 50 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	true_consecutive_calls	350.2 ns	294.7 ns	+18.85%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing wtcpython:who-windows (30b8f55) with main (f604ab9)²}

Footnotes

1. 50 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (51ed5dc) during the generation of this report, so f604ab9 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/expand/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/tail/tail-n0f is now passing!