Add a common backend for running librespeed-cli measurements on a router.
The package provides a locked measurement runner, live progress state, and
an rpcd ucode plugin exposing start/stop/status/result/history/config over
ubus. Scheduled measurements are managed through cron and can run within a
configurable time window. Optional daily aggregation keeps longer-term
history compact.
Raw measurements are kept in JSONL for a configurable retention period.
When persistent archive storage is configured, completed days are reduced
to daily min/avg/max values.
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
