more tests (more bugs)

kept going with the unit tests

the test suite now covers most of the important stuff, including:

• ECS / entity IDs / UUIDs
• serialization + hierarchies
• collision geometry, events and movement
• maps
• animation
• saves
• ObSL + some EngineLib bindings
• assets / asset lifetime
• VFS + packaged projects
• configuration
• editor undo commands

also added a couple integration tests for audio and rendering (OpenGL tests are optional)

finding things

unsurprisingly this found some actual problems too.

stale entity handles can no longer remove / access components from an entity that reused the same slot, and editor undo commands are a bit safer around entities or components disappearing.

also fixed some hierarchy rotation decomposition weirdness, cleaned up VFS / package mounting state so old package data can’t leak into the next mount, and added a few other small null / cleanup checks around scenes and rendering resources.