Track `interesting_origin` correctly in `fuzz_one_input`

[Liam-DeVoe]

interesting_origin is set by mark_interesting, normally called by _execute_once_for_engine, which sits above state.execute_once in the stack. Because fuzz_one_input calls state.execute_once directly, data.interesting_origin is always None. We should replicate the InterestingOrigin instantiation logic in fuzz_one_input, instead of relying on data.interesting_origin.

Also: test that the observability reports written by fuzz_one_input contain the correct interesting_origin (they don't currently, for this reason).

This means fuzz_one_input is not currently saving anything beyond the first found failure to the database.