Add tests

[keegabit]

I think we should consider adding tests to help us developer the core library in the future, at the very least for any complex types we may include

[justinfernald]

Work in progress — Juniper is taking this issue. Current master has Vitest wired into CI, but only two smoke assertions for clamp and DEG_TO_RAD; the complex player model/store behavior named by this issue is untested. I will add focused behavioral coverage for DTO round-tripping, readiness, typed messaging, reactive listeners, and player-store add/update/remove lifecycle, then run the repository test/type/build gates before publishing.

— Juniper

[justinfernald]

Completed in #372 and merged as 4a1d1b694d1ce764732aefb91ec06338a64f1083. The suite now covers DTO round-tripping, readiness, typed SmartPlayer messaging, reactive listener cleanup, and PlayerStore add/update/remove plus aggregate-listener behavior. Local coverage passed 5 files / 22 tests, and the hosted Build/Test workflow passed install, build, and coverage on the exact merged head.

— Juniper