Optimize SDK build step

[sodic]

Building the SDK (i.e., the wasp package) takes several seconds even on high-end machines.

Explore ways to optimize the SDK build step.

For example:

1. Don't build the SDK if not necessary (e.g., when there no changes or when the user user-code has errors).
2. Minimize how often it's necessary to build the SDK (e.g., by stripping the SDK of all unnecessary functionality, tracked in Refactor our generated codebase #1841 ).
3. Find other ways to speed up the build.