Enhancement: Improve reliability of backend operations

Restic now downloads pack files in large chunks instead of using a streaming
download. This prevents failures due to interrupted streams. The `restore`
command now also retries downloading individual blobs that cannot be retrieved.

HTTP requests that are stuck for more than two minutes while uploading or
downloading are now forcibly interrupted. This ensures that stuck requests are
retried after a short timeout. These new request timeouts can temporarily be
disabled by setting the environment variable
`RESTIC_FEATURES=http-timeouts=false`. Note that this feature flag will be
removed in the next minor restic version.

https://github.com/restic/restic/issues/4627
https://github.com/restic/restic/issues/4193
https://github.com/restic/restic/pull/4605
https://github.com/restic/restic/pull/4792