test(peer-cli): expand streamed install edge coverage

NEXT_STEPS item 6 called for the remaining streamed-install edge cases to
be covered in the peer-cli matrix. Add S43-S47 for already-installed
rejection, corrupt archive rollback, sender disconnect, receiver cancel,
and sorted multi-archive streaming.

The receiver-cancel scenario needs the harness to drive the same runtime
path as the GUI, so `lanspread-peer-cli` now accepts a narrow
`cancel-download` command that forwards to `PeerCommand::CancelDownload`.
A parser test covers the new JSONL command shape.

Add `fixture-multi/cnctw`, a tiny two-archive RAR fixture. S47 uses it to
prove streamed installs process root `.eti` archives in sorted order and
commit only extracted `local/` payloads, not the root archives or
`version.ini` sentinel.

Test Plan:
- just fmt
- python3 -m py_compile crates/lanspread-peer-cli/scripts/run_extended_scenarios.py
- python3 crates/lanspread-peer-cli/scripts/run_extended_scenarios.py S43 S44 S45 S46 S47 --build-image
- just test
- just clippy
- git diff --check
- git diff --cached --check

Refs: NEXT_STEPS.md item 6

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