[DG-Elom]

Part of #808 (point 1: a clearer error when unrar fails).

Previously a failure reported by unrar was shown as e.g.

[ERROR] Unexpected error in rar archive
 - Could not create file

without the entry concerned nor any hint. This maps unrar's Code/When to a descriptive message with hints (file name too long / permissions for ECreate, corrupted archive for BadData/BadArchive, missing or wrong password -> --password, etc.) and reports the archive entry being extracted:

[ERROR] failed to extract "aaaa…"
 - could not create the output file

hint: The file name might be longer than the file system allows (usually 255 bytes)
hint: Also check the write permissions and the free space of the destination directory

Adds a UI snapshot test with a small RAR5 fixture (350 bytes, stored) whose single entry name is 300 bytes, which triggers ECreate. Other codes fall back to unrar's own text when not mapped.

Tested with --no-default-features --features unrar,use_zlib,use_zstd_thin (bzip3 needs libclang, which I don't have locally) and without the unrar feature; clippy and nightly rustfmt are clean.

Not covered: skipping failing entries and extracting a single file (points 2 and 3 of the issue).