Extract registerAirNodes and registerWaterNodes lambdas to deduplicate node registration

Replaces 5 repeated air-node registration blocks (each ~20 lines of
GetOnlySingleNode + TestCompSet boilerplate) and 3 water-node registration
blocks with concise single-line helper calls.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: lefticus