feat(zip): checkhealth and encrypted entries

Problem:
There is no health check. Encrypted entries cannot be read at all, since
Info-ZIP takes a password only from a terminal and `-P` would expose it
in the process arguments.

Solution:
Add `:checkhealth nvim.zip`, reporting the backend and which
implementation is handling archives. Prompt for the password on a pty,
extracting to a file so the entry's bytes stay off the terminal. Report
Info-ZIP's exit code rather than inferring a cause, so an archive using
AES is not reported as a failed decryption.

0 files changed, 0 insertions, 0 deletions