docs: mark #125 FD-ownership hazard resolved in roadmap 8.1

[leynos]

Summary

Roadmap Section 8.1 previously bundled issues #124 and #125 into a single outstanding "pump file-descriptor close race" work item. The #125 panic-unwind FD ownership hazard is now fixed in code and regression-tested, so this documentation-only change stops presenting it as outstanding implementation work.

Changes

• Record #125 as resolved: with_borrowed_reader wraps the borrowed reader in ManuallyDrop, keeping a caller-owned reader FD open on both success and panic-unwind; pump_stream/consume_stream route through the helper; and rust/cuprum-rust/src/lib_tests.rs regression-tests that the borrowed FD survives normal and panicking operations.
• Rescope task 8.1.1 (the silent Bad file descriptor shutdown close race) to the still-outstanding #124.

Verification

make markdownlint and make nixie both pass (docs-only diff).

🤖 Generated with Claude Code

Summary by Sourcery

Documentation:

• Clarify roadmap section 8.1 to mark issue Rust: extract FD-borrow RAII helper to centralise mem::forget ownership contract #125 as resolved and explicitly scope task 8.1.1 to the outstanding Bad file descriptor shutdown race in Rust: fold split-first-iteration splice duplication into one loop; fix drain_reader EINTR handling #124.

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[leynos]

Superseded by #232. The branch was renamed to issue-125-rust-extract-fd-borrow-raii-helper-to-centralise-mem-forget-ownership-contract, which closed this PR; the review continues on #232.