Switch to isolated declarations for faster builds

[kenotron]

This is a small repo, so it isn't strictly necessary. However, isolated declarations is giving us a 14.59s -> 5.43s improvement in typechecking. This change includes the following:

1. added an isolated-declarations flag to the main tsconfig.json: this means no allowJS
2. replacing the type check step from using a tsc worker to simply using tsc processes
3. adjusted the lage pipeline config to allow fastest parallelized builds possible.