Ignore overlayplugin data, but have it defined in ActEventType

[nonowazu]

While it's set to noop now, having it defined keeps us from getting raised events when raise_on_invalid_id is True

For more information in this addition, see cactbot docs

[ayyaruq]

Alternative idea: could we instead generic >255 is an extended event and ignore that way? I feel like there's a difference between intentionally no-oping ACT events, and ignoring extensions that aren't part of ACT in the first place. We also have absolutely no guarantee that 256 is purely for OverlayPlugin - any other plugin could recycle the same ID if they wanted to.

[nonowazu]

If we nooped like that, it would have to go in the parser before we check to see if the ID is in the enum. We'd probably need to check to see if 256 is some "universal other" field, however – I don't like the idea that we might one day get a 257 that we actually care about and then have to rearchitect around that.