fix: prevent destructive overwrite of decompression directories

[fzlzjerry]

Closes #1043.

Summary

• remove the destructive overwrite choice when a decompression conflict target is a directory
• keep rename, merge, and skip for directory conflicts while preserving overwrite for actual file conflicts
• update the multi-format merge coverage and add regressions for preserving unrelated directory contents and overwriting a single-file target
• document the fix in the changelog

Validation

• cargo test --locked
• cargo test --locked --no-default-features
• cargo test --locked --no-default-features --features unrar,use_zlib,use_zstd_thin
• cargo clippy --locked --all-targets -- -D warnings
• cargo clippy --locked --no-default-features --all-targets -- -D warnings
• cargo +nightly fmt -- --check

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[marcospb19]

review requested due to automatic review settings

wat, uh, oke, Imma ignore that

[marcospb19]

remove the destructive overwrite choice when a decompression conflict target is a directory

Did you choose that by accident and had an unintended deletion? Do you think the conflict message was confusing and could be improved?

[fzlzjerry]

No, I did not lose data myself; I reproduced the behavior reported in #1043. The prompt says overwrite, but for an explicit --dir it does not make clear that this recursively removes the entire existing destination, including unrelated contents. The reporter expected archive collisions to be overwritten and lost unrelated projects, which is why I removed the directory-level option. If you prefer to keep it, I can narrow the patch to an explicit destructive warning/confirmation instead.