v0.6.0

Changes:

• activation: fix build for compatibility with newer nix
• cargo: bump MSRV to 1.56
• ci: update workflow
• credentials: add helpers for accessing credential data
• daemon/notify: add support for abstract Unix sockets
• daemon/notify: add support for sending file descriptors
• daemon/notify: sanity-check state entries
• errors: add internal helpers to simplify error handling
• id128: add get_boot() and get_boot_app_specific()
• logging: use std API to extract journal stream from FD
• logging: fix connected_to_journal() logic
• logging: only check stderr for protocol upgrading
• logging: reduce the amount of allocations in hotpath
• logging: un-export some JournalStream methods