Download the tdlib_json_cli binary pinned in priv/tdlib/manifest.json
into the per-user cache, verifying its sha256. Idempotent; no-op when
config :sexy, :tdlib_binary (or SEXY_TDLIB_PATH) is set.
Sexy.TDL does this automatically at startup — run the task explicitly to
prefetch, e.g. in CI or a Dockerfile, so first boot needs no network:
mix sexy.tdl.install