Initial data logging implementation. (#41)

Similar approach to radio.

Add tests with vitest. At some point we'll try to switch to vite to
build this so pick an aligned test runner.

Author: microbit-matt-hillsdon

ci-build.sh

@@ -12,4 +12,4 @@ git clone https://github.com/emscripten-core/emsdk.git ~/.emsdk
 ~/.emsdk/emsdk activate latest
 source ~/.emsdk/emsdk_env.sh
 
-npm run build
+npm run test && npm run build