Add the ability to decrypt media content with the shaka-packager helper application running in its official Docker/Podman container (instead of installed locally on the host), and with the MP4Box helper application from the official GPAC Docker/Podman container. These rely on a container runtime (Podman or Docker) being installed. The container runtime to use can be specified using the DOCKER environment variable (defaults to podman; it will only work with Docker if it is configured for rootless operation, or you will encounter file ownership problems).
Improve support for dynamic manifests that use SegmentTemplate+SegmentTimeline addressing.
Improve handling of manifests without a MPD.mediaPresentationDuration attribute and without a Period.duration attribute.
Clean up the temporary file used to invoke the decryption helper mp4box.
Use human-readable formatting when displaying per-Period duration information.
Replace the unmaintained backoff crate by the backon crate.
Replace the unmaintained dev dependency json by the jzon crate.