fix(rust-sdk): tag agent/crawl/batch/map/parse requests with SDK origin

Agent requests sent no origin at all, making them indistinguishable from
raw API traffic server-side; crawl, batch scrape, and map lacked the
field entirely, and parse had it but never injected it. All now default
to rust-sdk@<version>, matching the other SDKs and the existing scrape
and search behavior. A caller-provided origin is still respected.

Bump to 2.16.1.