Port all existing `event.rs` files to use proto events.

[hdevalence]

Following the work in #3460 to define protobuf event handling, it would be good to convert the existing events:

We should then replace all existing events defined in the Penumbra application with Protobuf-based events. These events should be defined in the Proto module corresponding to the component that emits the event. Currently, there are only 12 events currently defined (VS Code search fn in files named event.rs), so this shouldn't be a huge lift.

Since any Protobuf message could in principle be encoded as an event this way, we should adopt a naming convention to distinguish messages defining events from messages defining other data. One possibility would be to name all of the event messages Event*. Using a prefix rather than a suffix means that all of the events will be grouped together when messages are sorted alphabetically.

In particular, porting over the DEX events will make them useful for trading bots (cf https://discord.com/channels/824484045370818580/1163684711667867678/1181748568135061514 )