In preparation for the proxmox-backup-client look-ahead caching,
where a passing around of different encoder instances with internal
references is not feasible.
Instead of creating a new encoder instance for each directory level
and keeping references to the parent state, use an internal stack.
Adds additional helper functions to solve borrow issues, when both
the state and writers have to be accessed by a mutable reference.
This is a breaking change in the pxar library API.
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
add a pxarcmd test example
make 'failure' an optional dependency as we only use it in
examples right now.
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
