Create a CLI tool to decrypt a CXP export/backup

This CLI should be useful for both testing purposes and for users who have a backup and want to inspect it. I should take the export archive and either the pre-shared-key or the "importing provider's" private key to decrypt and (optionally) deserialize the format.

For users this can be usefull to recover from a provider that went under and their new provider does not support CXP/CXF yet.

For developers, this can be usefull to diagnose any issues in their implementation for either the protocol or the format.

Start by reading the repository's existing Credential Exchange implementation and determining how CXP/CXF archives and the pre-shared-key or importing provider's private key are represented. Done means a CLI can accept an export archive, decrypt it with either supported key type, and optionally deserialize the result for user recovery and developer diagnostics.

Written by the indexing model from the issue text.