reconsider the Action dynamic dispatch

Consider using https://crates.io/crates/enum_dispatch instead of dynamic dispatch, or if I decide to value the ability to have users of this crate be able to implement their own `Action`s for the system, then figure out a way to remove the `ActionType` enum and replace it with something else, perhaps an integer order priority method for the `Action` trait.

The issue names the Action trait and ActionType enum but no files or tests. Start by locating their definitions and the current dynamic-dispatch entry points, then compare the available designs, including enum_dispatch and support for user-defined Actions. Done requires a decided dispatch design with its compatibility implications established.

Written by the indexing model from the issue text.