Runs an ad-hoc YARA rule against the historical object corpus and
returns the matches. Combines two discovery paths automatically:
candidate-file lookup using Stairwell's partial binary indexes,
and variant discovery for any SHA256/SHA1/MD5 literals named in
the rule body. Results are returned synchronously when the scan
finishes or when max_matches is reached.

The scan's environment scope is controlled by the request's
environments field — an empty list means "every environment the
caller can read." The rule is NOT persisted; use CreateYaraRule
for that. This endpoint is for quick evaluation of a rule body
against history.