feat: cancelable operations + stable error codes

[cursor]

Motivation

Large archives can run for a long time with no way to abort. Competitors (react-native-nitro-unzip, react-native-unarchive) already expose cancellation. Error handling is also inconsistent across platforms (generic messages, historically null codes), which makes UI branching hard.

Proposal

cancel(): Promise<void>

Cancel the in-flight zip/unzip operation (best-effort). Reject the active promise with a stable CANCELLED code. Clean up partial output where practical.

Stable error codes

Reject with a consistent code string on both platforms, e.g.:

Code	When
ERR_FILE_NOT_FOUND	Source missing
ERR_INVALID_PATH	Bad destination / empty path
ERR_WRONG_PASSWORD	Password decrypt failed
ERR_CORRUPT_ARCHIVE	Not a zip / truncated / bad CRC
ERR_UNSAFE_PATH	Zip Slip / symlink escape
ERR_CANCELLED	User cancelled
ERR_BUSY	Operation rejected because another is running (if serialized)
ERR_ZIP / ERR_UNZIP	Generic fallback

Acceptance criteria

• cancel() stops in-flight zip and unzip on iOS and Android
• Cancelled promise rejects with ERR_CANCELLED
• Existing failure paths map to the table above (no null codes)
• Documented in README + TypeScript types for known codes
• Tests cover cancel mid-unzip and wrong-password mapping

Priority

P0