refactor: replace rustix::process dependency with rlimit

[xtqqczze]

Closes #14914.
Reverts #14664.

[sylvestre]

sorry but i am not going to revert anything until we have a CI running for redox

[oech3]

I think we don't need to revert this since we were not running test(impossible?) for Redox on the CI previously.

[xtqqczze]

I think we should add a check-only job at the very least:

cargo check --all-targets --features feat_os_unix_redox --target x86_64-unknown-redox

We can set continue-on-error: true for now so that any existing errors don’t block CI, while still giving us visibility into Redox build issues.

[sylvestre]

Sounds good

[oech3]

Do we really need to hurry supporting test on redox? Most logic are shared with other platforms.

[codspeed]

Merging this PR will improve performance by 56.76%

⚠️ 64 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• du_summarize_balanced_tree[(5, 4, 10)]
• du_wide_tree[(5000, 500)]
• cksum_raw_output
• cksum_crc32b
• cksum_crc
• cksum_default
• cksum_multiple_files
• factor_multiple_u64s[2]
• dd_copy_64k_blocks
• du_all_wide_tree[(5000, 500)]
• …and 54 more

⚡ 2 improved benchmarks
✅ 111 untouched benchmarks
⏩ 342 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	three_39_bit_primes	591.3 ms	260.7 ms	×2.3
⚡	thirteen_39_bit_primes	9.6 s	8.9 s	+8.34%

Tip

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

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_{Comparing xtqqczze:GH14664 (8bfe21f) with main (8b27533)²}

Footnotes

1. 342 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 (c5a3ce5) during the generation of this report, so 8b27533 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[oech3]

If we replaced rustix with rlimit, we need large diff again to remove it after rustix supported rlimit on redox.