feat(dl): add --sample and --include-sample

--sample downloads only a time window of a title (default 120-180 s) and cuts the mux to it. --include-sample cuts a 60 s sample from a finished file. Both write to a Sample folder with a SAMPLE tag on the filename

docs/dev/rest-api/endpoints.md

@@ -462,6 +462,8 @@ Make a download job. It requires `service` and `title_id`. Every other field is
 | `cdm_only` | boolean | `null` | Force CDM-only (`true`) or vault-only (`false`) key retrieval. |
 | `proxy` / `no_proxy` / `no_proxy_download` / `proxy_download` | string / bool / bool / string | `null` / `false` / `false` / `null` | Proxy controls. `proxy` and `proxy_download` must be full proxy URIs unless the API key has `server_proxy`. A Control D resolver, `controld://<resolver>@dns.controld.com`, counts as a full proxy URI: the server runs a forwarder for it. |
 | `no_folder` / `no_source` / `no_mux` | boolean | `false` | Output/mux controls. |
+| `sample` | boolean/string | `null` | Download a short sample and write it with a `SAMPLE` tag on the filename in a `Sample` folder inside the output folder. `true` is 60 seconds from 2 minutes in; `"0-60"` is a window in seconds. |
+| `include_sample` | boolean | `false` | Download the full title, then also cut a 60 second sample from each muxed file into a `Sample` folder next to it. |
 | `workers` | int | `null` | Threads per track. |
 | `adaptive_workers` | boolean | `false` | Scale segment workers to measured CDN throughput, up to the `workers` cap. |
 | `download_processes` | int | `1` | Split a track's segments across this many processes. Only engages for large batches. |