Mark Many As Read Partial Parse

mark-many-as-read experiment now triggers during discovery

With the mark-many-as-read experiment enabled, a unit whose terraform { source = ... } pointed at a local module did not show up under --filter 'reading=' filters that referenced files inside that module. Discovery would parse the unit, but the module files were never recorded as read, so the reading filter attribute could not match and the queue came back empty.

The module walk now runs on the discovery code path as well, so changes to files in a local module source flow through to the units that depend on them.