Events stream in via model_write listener while also being fetched
from the database. If the DB fetch completed before all events were
persisted, replaceModelsInStore would wipe out events that came in
via model_write.
Added mergeModelsInStore that adds fetched events without removing
existing ones. Applied to HTTP, gRPC, and WebSocket event hooks.
Previously, when a gRPC streaming message failed to deserialize (e.g., wrong
type like int instead of string), the error was silently logged and the message
was dropped. Now errors are surfaced to the UI as GrpcEventType::Error events.
Changed the streaming/client_streaming methods to accept an on_message callback
that handles both success (logs ClientMessage) and error (logs Error) cases,
rather than logging the client message prematurely before deserialization.
The gRPC streaming code was using tokio::runtime::Handle::current().block_on()
inside filter_map closures, which caused a panic ('Cannot start a runtime from
within a runtime') when called from an async context.
Fixed by replacing the pattern with .then(async move { ... }).filter_map(|x| x)
which properly handles async operations in stream pipelines.
This fixes the gRPC Ping/Pong freeze issue and restores request cancellation.
