Cannot import other source files when running in `zinniad`

[bajtos]

See CheckerNetwork/node#727 (comment)

[2025-04-23T11:47:15Z ERROR zinniad] Cannot canonicalize module path: No such file or directory (os error 2).
    Module file path: /ZINNIA/lib/spark.js
    Module URL: file:///ZINNIA/lib/spark.js
    Imported from: file:///home/node/.cache/checker-network-node/subnets/sources/spark/main.js
Reporting the problem to Sentry for inspection by the Checker team.
Zinnia main loop errored ExecaError: Command failed with exit code 1: /usr/src/app/runtimes/zinnia/zinniad spark/main.js