feat: observables in model diagram

[shawnyama]

Description

• A new observableSummary object is used to create observable nodes and edges in mira.ts

graph.ts

• In graph.ts I first set nodes and edges for the states and transitions (skipping observables)
• Once they are set I can determine where the "right" of the graph is so I can start setting the positions of the observable nodes
• Then I draw custom edges from the observable nodes to the states that they are attached to
• I also did some cleanups in graph.ts such as using forEach instead of for of

petrinet-renderer.ts

• added observable nodes/edges graphics here
• added mouse-enter and mouse-leave events to focus on observable nodes/edges when the node is hovered on

https://github.com/DARPA-ASKEM/terarium/assets/28237258/562043ef-8548-4abf-a2f6-6f12b03c0ebb