wasi: clean up core platform abstractions

[DePasqualeOrg]

This is the first PR split out from the larger WASI changes in #11712.

Changes

• Use rustix::fs::Stat for WASI FileInformation so same-file checks use device/inode identity instead of a file-type/size heuristic.
• Make read_fs_list() return UResult<Vec<MountInfo>> on WASI, matching other platforms while still returning an empty mount list.
• Use the WASI-specific OsStrExt/OsStringExt imports in env.
• Add inert WASI tail process-check stubs so the shared follow code compiles while --pid remains unsupported.
• Remove an unreachable nested cfg branch from non-WASI OwnedFileDescriptorOrHandle::into_stdio().
• Update WASI comm tests for corrected same-file detection.

[oech3]

closes #12427

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Note: The gnu test tests/cut/cut-huge-range is now being skipped but was previously passing.

[sylvestre]

please refactor to avoid the allow dead code

[DePasqualeOrg]

Okay, I think we can just remove ProcessChecker for WASI. Since the original PR is from a couple months ago, I don't remember why exactly it was added.

[codspeed-hq]

Merging this PR will degrade performance by 3.66%

⚠️ 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
❌ 3 regressed benchmarks
✅ 319 untouched benchmarks
⏩ 46 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	cp_recursive_deep_tree[(120, 4)]	562.5 KB	615.6 KB	-8.62%
❌	Simulation	ls_recursive_balanced_tree[(6, 4, 15)]	49.6 ms	52.3 ms	-5.2%
❌	Simulation	ls_recursive_wide_tree[(10000, 1000)]	33 ms	34.3 ms	-3.81%
⚡	Simulation	single_date_now	85.5 µs	82.7 µs	+3.38%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing DePasqualeOrg:wasi-core-platform-abstractions (2645a6d) with main (4505d51)}

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. ↩