fix(wasi): date clock resolution and system datetime support

[eduardomourar]

date implements get_clock_resolution via libc::clock_getres (rustix's excludes WASI) and set_system_datetime for WASI, the latter reporting "not supported" since the sandbox has no wall-clock-set syscall.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/unexpand/bounded-memory is now passing!

[codspeed-hq]

Merging this PR will improve performance by 3.49%

⚠️ 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

⚡ 2 improved benchmarks
✅ 343 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	sort_long_line[10000]	1.2 ms	1.1 ms	+3.68%
⚡	Simulation	numfmt_to_si_precision[10000]	93.3 ms	90.3 ms	+3.3%

Tip

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

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_{Comparing eduardomourar:wasi-date-fixes (2321086) with main (bad4676)²}

Footnotes

1. 46 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 (0c8a3c7) during the generation of this report, so bad4676 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩