Refactor string enums to integer representations, add optional snippet optimizations

[shanemadden]

To do:

• Change to int repr and implement snippet-based conversion for Part
• Change to int repr and implement snippet-based conversion for StructureType
• Change to int repr and implement snippet-based conversion for ResourceType / IntershardResourceType / MarketResourceType
• Change to int repr and implement snippet-based conversion for PowerCreepClass
• Implement snippet-based conversion for ObjectId / RawObjectId
• Implement snippet-based conversion for RoomName
• Implement snippet-based conversion for Direction (when encountered in string form, eg. in describe_exits() return)
• Add tests for all conversions including benchmarks if practical
• Add wasm-pack test --node to GH actions test toolchain

Resolves #230

[shanemadden]

string enums have int reprs automatically in wasm-bindgen 0.2.93; no longer need some of this, but other parts will still be useful.