API: Fix load exception handling

Models do not fully unload if an exception is caught in load. Therefore,
leave it to the client to unload on cancel.

Also add handlers in the event a SSE stream is cancelled. These packets
can't be sent back to the client since the client has severed the
connection, so print them in terminal.

Signed-off-by: kingbri <bdashore3@proton.me>

utils.py

@@ -14,9 +14,9 @@ class TabbyGeneratorErrorMessage(BaseModel):
 class TabbyGeneratorError(BaseModel):
     error: TabbyGeneratorErrorMessage
 
-def get_generator_error(exception: Exception):
+def get_generator_error(message: str):
     error_message = TabbyGeneratorErrorMessage(
-        message = str(exception),
+        message = message,
         trace = traceback.format_exc()
     )