fix: handle empty dict handler response without KeyError

[AmSach]

Bug Summary

When a Runpod handler returns an empty dict {}, the framework raises a KeyError in the FastAPI development endpoint.

Root cause: In rp_job.py, when a handler returns {}, the 'output' key gets removed before the result is returned (line ~207). However, in rp_fastapi.py, both _sim_runsync() and _sim_status() unconditionally access job_output['output'] at the return statement, causing a KeyError.

Fix

Changed job_output['output'] to job_output.get('output') in two locations:

• _sim_runsync() (line 342)
• _sim_status() (line 419)

This gracefully returns None when the 'output' key is absent, making the behavior consistent with documented expectations (returning {} from a handler is valid).

Testing

Verified by analysis of the code flow:

1. Handler returns {}
2. rp_job.py sees run_result.get('output') == {} and calls run_result.pop('output')
3. run_result becomes {}
4. Back in rp_fastapi.py, job_output = {}
5. Before fix: job_output['output'] → KeyError: 'output'
6. After fix: job_output.get('output') → returns None, serialized as null

Fixes #459