[Bug] Missing Handlers for Defined Event Undetected During Compilation

[itsjerryokolo]

Bug report

Deploying a subgraph to the studio with an event listed in the manifest but its handler not defined in the mapping file causes it to fail at runtime. Detecting this issue during deployment would make debugging easier and improve the developer experience.

[lutter]

This is really a graph-cli issue - it should already warn about the missing handler before the subgraph is deployed. THe most elegant way to address this would be through this issue